495

495 = 3² x 5 x 11.

495 is the Kaprekar constant for three-digit numbers. Arrange the digits of any three-digit number whose digits are not all the same in descending and ascending order, compute the difference, then repeat the process. For example: 311 - 113 = 198; 981 - 189 = 792; 972 - 279 = 693; 963 - 369 = 594; 954 - 459 = 495.

495 is the ninth pentatope number.

495 is a number that cannot be written as a sum of three squares.

Interstate 495 (Capital Beltway) is a highway that surrounds Washington, D.C.

Source: Wolfram MathWorld

443

443 is a prime number. It is the 24th Sophie Germain prime: 443 x 2 + 1 = 887, which is also prime.

443 is the first three-digit non-palindromic prime number whose binary equivalent (110111011) is a palindromic prime in base 10.

The sum of the digits of 443 is a prime: 4 + 4 + 3 = 11. Hence, 443 is an additive prime

443 is the smallest prime containing exactly two 4s.

Telephone area code 443 includes Baltimore, Md.

Source: Prime Curios!

300

300 = 2² x 3 x 5².

300 is a triangular number, the sum of all positive integers up to 24: 1 + 2 + 3 + . . . + 22 + 23 + 24 = 300.

300 is the sum of twin primes: 149 + 151 = 300.

300 is a number n such that n² (90000) contains exactly two different digits.

In bowling, 300 is the largest possible score.

Source: Wolfram MathWorld

255

255 = 3 x 5 x 17.

255 = 11111111 in base 2.

255 is the largest value representable as an 8-bit binary number. Eight bits, otherwise known as a byte, is a very common size for storing "small" values in computer memories. Consequently, 255 appears as a bound or an otherwise magic number in many computer-related tasks. For example, 255 is the maximum amount of red, green, or blue that goes into an RGB color, as well as the maximum content of any of the four octets of an IP address.

255 is the least odd integer greater than 3 that is not the sum of two distinct powers of two and a prime.

255 is a number that cannot be written as a sum of three squares.

255 is 3333 in base 4.

255 is a Mersenne number: 255 = 2⁸ - 1.


Source: Number Gossip

249

249 = 3 x 83.

The sum of the digits of 249 equals five times the number of digits: 2 + 4 + 9 = 15 = 3 x 5.

249 is a number not divisible by any of its digits.

249 is a Blum number. A natural number n is a Blum integer if n = pq is a semiprime (the product of two prime numbers) for which p and q are distinct prime numbers congruent to 3 mod 4. That is, p and q must be of the form 4t + 3, for some integer t.

249 Ilse is an asteroid with an unusually slow rotation period, discovered in 1885.

Source: The On-Line Encyclopedia of Integer Sequences

146

146 = 2 x 73.

The absolute difference between any two digits of 146 is a prime number (2, 3, 5).

146 is 222 in base 8.

146 is an octahedral number, which has the form (2n³ + n)/3.

146 is an untouchable number: No integer's proper divisors add up to 146.

146 has a representation as a sum of two squares: 146 = 5² + 11².


The Grand Union Canal Race is a 146-mile ultramarathon from Birmingham to London.

Source: Prime Curios!

91

91 = 7 x 13.

91 is the first non-trivial odd composite number. Every smaller composite is either even, a familiar square, ends in 5, has a digit sum that is a multiple of 3, or is obviously divisible by 11.

91 is the sum of the squares of the first six integers: 1² + 2² + 3² + 4² + 5² + 6² = 91. It is the 13th triangular number.

91 is the sum of the first 13 positive integers: 1 + 2 + 3 + . . . + 11 + 12 + 13 = 91.

91 has a unique representation as a sum of three squares: 91 = 1² + 3² + 9².

91 is 111 in base 9.

91 cents is the total amount of money one has, given one each of a penny, nickel, dime, quarter, and half dollar.
Source: Number Gossip

51

51 = 3 x 17.

51 is the smallest number that can be written with all the digits from 1 to 5 (without repetition) as a sum of prime numbers: 2 + 3 + 5 + 41 = 51. Note that the highest digit (5) and the lowest digit (1) are the digits of 51.

51 is a pentagonal number, a number of the form n(3n - 1)/2, and a centered pentagonal number (one of the few numbers to be both).

51 is 110011 in base 2 (binary) and 33 in base 16.

51 is the sixth Motzkin number.

Area 51 is a nickname for a secret military base located in the southern portion of Nevada in the western United States.

Source: Prime Curios!

47

47 is a safe prime number. A safe prime has the form 2p + 1, where p is also a prime.

There are 47 occurrences of 47 in the first thousand prime numbers.

4³ + 7³ = 407.

47 is the smallest number n for which 666ⁿ has a digit sum of 666.

The atomic number of silver is 47.

Sources: Number Gossip; Prime Curios!

711

711 = 3² x 79.

711 is the concatenation of the fourth and fifth primes.

711 is a number that cannot be written as a sum of three squares.

711 is a divisor of 80² - 1.

711 is the sum of ten positive fifth powers: 711 = 3⁵ + 3⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 1⁵.

711 is the phone number of the Telecommunications Relay Service, commonly used by the deaf and hard-of-hearing.

The logo for a chain of convenience stores.

#711 was a comics superhero created by George Brenner and published by Quality Comics from 1941 to 1943.

In the 1950 movie 711 Ocean Drive, a telephone repairman in Los Angeles uses his knowledge of electronics to help a bookie set up a betting operation.

Source: WolframAlpha

692

692 = 2² x 173.

692 is a number that has no digits in common with its cube (331373888).

692 has a representation as a sum of two squares: 692 = 4² + 16².

692 is a member of the sequence generated when you start with 1, then repeatedly multiply by 5 and reverse the digits: 1, 5, 52, 62, 13, . . . , 592, 692, 643, . . .


In Microsoft Windows, error 692 signals a "hardware failure in port or attached device."

The U.S.S. Allen M. Sumner (DD-692), a destroyer, served in the U.S. Navy from 1943 to 1973.

1225

1225 is the product of the square of 5 and the square of 7 and hence is the square of 35. It is the product of the squares of two consecutive primes, 5 and 7.

1225 has a representation as a sum of two squares: 1225 = 21² + 28².

1225 is the smallest number with three representations as a sum of four positive cubes: 1225 = 1³ + 2³ + 6³ + 10³ = 3³ + 7³ + 7³ + 8³ = 4³ + 6³ + 6³ + 9³.

1225 is a triangular square number; it is both a perfect square and a triangular number. 1225 is also a hexagonal number.

A representation of consecutive hexagonal numbers.

Pere Marquette 1225 is a steam locomotive.

Source: Wolfram MathWorld

105

"Every number is built by multiplying prime numbers—105, for example, is three times five times seven. They are like the atoms of arithmetic—the hydrogen and oxygen of the world of numbers."—Marcus du Sautoy, The Guardian, Nov. 1, 2008.

105 is the 14th triangular number. It is the sum of consecutive integers: 1 + 2 + 3 + . . . + 13 + 14 = 105.

105 is the sum of consecutive integers in four other ways: 12 + 13 + . . . + 17 + 18 = 15 + 16 + 17 + 18 + 19 + 20 = 19 + 20 + 21 + 22 + 23 = 34 + 35 + 36 = 52 + 53.

Paul Erdös conjectured that 105 is the largest number n such that the positive values of n - 2^k are all prime: 105 - 2 = 103, 105 - 4 = 101, 105 - 8 = 97; 105 - 16 = 89; 105 - 32 = 73; 105 - 64 = 41.

105 is 77 in base 14.

Space Shuttle Mission STS-105 was launched into space on Aug. 10, 2001.

Source: Wolfram MathWorld

2929

2929 = 29 x 101.

2929 has two representations as a sum of two squares: 2929 = 15² + 52² = 25² + 48².

2929 is the hypotenuse of two primitive Pythagorean triples: 2929² = 1560² + 2479² = 1679² + 2400².

2929 is a square-free number because its prime decomposition contains no repeated factors.

2929 is a divisor of 100¹⁴ - 1.

2929 Entertainment is a media company with interests ranging from movie production to video games.

Source: Number Gossip

1875

1875 = 3 x 5⁴

1875 is an economical number.

1875 is the smallest order for which there are 21 groups.

The product of the prime factors of 1875 plus one is a perfect square: 3 x 5 + 1 = 16 = 4².

1875 is a number n such that n - 4, n - 2, n + 2, and n + 4 are prime: 1871, 1873, 1877, and 1879 are all prime.


French mathematician Henri Lebesgue was born June 28, 1875.

Source: What's Special About This Number?

416

416 = 2⁵ x 13.

416 is the number of subsets of the 15th roots of unity that add up to a real number.

416 has a representation as a sum of two squares: 416 = 4² + 20².

416 is a number with exactly 12 divisors: 1, 2, 4, 8, 13, 16, 26, 32, 52, 104, 208, 416.


416 is the area code for the city of Toronto. It is one of the original 86 area codes from 1947.

Episode 416 (4th season, 16th episode) of the TV series Numb3rs was titled "Atomic No. 33" and included references to non-Newtonian fluids, the Riemann zeta function, and Bayesian network analysis.

Sources: What's Special About This Number?; The Math Behind Numb3rs

63

63 = 3² x 7.

63 = 6² + 3³ = 2⁶ – 1.

63 is the smallest number such that the common alphabetical value of its representation in Roman numerals is equal to itself: LXIII -- 12 + 24 + 9 + 9 + 9 = 63.

63 is a Harshad (or Niven) number; that is, it is divisible by the sum of its digits.

63 is the number of partially ordered sets of 5 elements.

63 is 333 in base 4.

M63 is a galaxy, known as the Sunflower Galaxy, in the constellation Canes Venatici.

Source: Number Gossip

145

145 = 5 x 29.

145 = 1! + 4! + 5! The only other numbers that are the sum of the factorials of their digits are 1, 2, and 40,585. These numbers are known as factorions.

145 is a pentagonal number and a centered square number.

145 is the sum of two squares in two different ways: 145 = 12² + 1² = 8² + 9².

145 is the hypotenuse of two primitive Pythagorean triples: 145² = 17² + 144² = 24² + 143².

Ted Williams hit 31 home runs and had 145 RBI as a rookie in 1939.

Source: Wolfram MathWorld

118

118 = 2 x 59.

118 is the smallest number that can be written as the sum of four triples, whose products are all equal: 118 = 14 + 50 + 54 = 15 + 40 + 63 = 18 + 30 + 70 = 21 + 25 + 72. The product of each triple is 37,800.

118 is the smallest three-digit composite number, all of whose other digit permutations are prime numbers: 181 and 811 are both prime.

118 is the sum of three positive cubes: 118 = 4³ + 3³ + 3³.

118 Peitho is an asteroid that was discovered in 1872.

Source: Number Gossip

74

74 = 37 x 2.

74 = 17 + 18 + 19 + 20.

74 is a hungry number. The kth hungry number is the smallest number n such that 2ⁿ contains the first k digits of the decimal expansion of pi: 5, 17, 74, 144, 144, 2003, . . . . The first number is 5 because 2⁵ is 32, which contains 3, the first digit of pi. They were named hungry numbers because they try to eat as much "pi" as possible.

74 has a representation as a sum of two squares: 74 = 5² + 7².

74 is the atomic number of tungsten.

Source: Number Gossip

56

56 = 2³ x 7.

56 is a pronic number because it is the product of two consecutive numbers: 7 x 8 = 56.

56 is the sum of the first six triangular numbers: 1 + 3 + .6 + 10 + 15 + 21 = 56. Hence, it is a tetrahedral number, the number of balls you can put in a triangular pyramid: 1, 4, 10, 20, 35, 56, 84, 120, . . .

56 is the sum of six consecutive prime numbers: 3 + 5 + 7 + 11 + 13 + 17 = 56.


56 men signed the Declaration of Independence in 1776, which led to the formation of the United States of America.

Source: Number Gossip

1111

1111 = 11 x 101.

1111 is the sum of the digits of the first 100 primes.

1111 is a number that cannot be written as a sum of three squares.

1111 is a divisor of 100² - 1.

1111 is n³ + n² + n + 1, for n = 10.

1111 is 787 in base 12.

Armistice Day, Nov. 11 (11/11), is the anniversary of the symbolic end of World War I in 1918, when the leaders of several countries signed an agreement on the 11th hour of the 11th day of the 11th month to cease hostilities.

Source: Number Gossip

77

77 = 7 x 11.

77 is the number of integer partitions of 12.

77 is the 22nd discrete biprime and the first of the (7.q) family. Since both 7 and 11 are Gaussian primes, this means that 77 is a Blum integer.

77 is the sum of three squares: 77 = 4² + 5² + 6².

77 is the sum of the first eight prime numbers: 77 = 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19.

During World War II in Sweden at the border with Norway, 77 was used as a password, because the tricky pronunciation in Swedish made it easy to instantly discern whether the speaker was native Swedish, Norwegian, or German.

Source: Wikipedia

508

508 = 127 x 2²

508 is the sum for four consecutive prime numbers: 113 + 127 + 131 + 137 = 508. It is also the sum of two successive primes: 508 = 251 + 257.

508 is a number that cannot be written as a sum of three squares.

508 is a member of the sequence generated by starting with 1 and repeatedly reversing the digits and adding two to get the next term: 1, 3, 5, 7, 9, 11, 13, 33, . . . , 605, 508, 607, . . .

508 is the area code for Worcester, Mass.

In the United States, section 508 of the Rehabilitation Act requires that Federal agencies give disabled employees and members of the public access to information that is comparable to the access available to others.

Sources: Wikipedia

85

85 = 5 x 17.

85 is a Smith number because the sum of its digits is equal to sum of the digits in its prime factorization: 8 + 5 = 13 = 5 + 1 + 7.

85 is a centered triangular number. Such a number can be represented by a dot in the center, with all other dots surrounding the center in successive triangular layers. The first few triangular numbers are: 1, 4, 10, 19, 31, 46, 64, 85, 109, . . .

85 is the largest known n for which 1² + 2² + 3² + . . . + n² = 1 + 2 + 3 + . . . + m has a solution.

There are 85 ways to tie a tie, according to a book by Thomas Fink and Yong Mao.

Sources: Wolfram MathWorld ; What's Special About This Number?

538

538 = 2 x 269.

538 has a representation as a sum of two squares: 538 = 3² + 23².

538 is the 10th open meandric number: 1, 1, 2, 3, 8, 14, 42, 81, 262, 538, 1828, . . .

538 is a number such that the sum of its odd digits equals the sum of its even digits: 5 + 3 = 8.

The Electoral College consists of 538 popularly elected representatives who formally select the President and the Vice President of the United States.

Source: WolframAlpha

435

435 = 3 x 5 x 29.

435 is a triangular number and a hexagonal number.

435 is the number of ordered partitions of 16 into distinct parts.

435 is the sum of seven positive fifth powers: 435 = 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 3⁵.

The United States House of Representatives has 435 members.

Source: The On-Line Encyclopedia of Integer Sequences

1103

1103 is a prime number. It is also a Sophie Germain prime. If both p and 2p + 1 are prime, then p is a Sophie Germain prime: 1103 and 2207 are both primes.

1103² = 1216609 and 3011² = 9066121.

1103 is the number of graphs with 9 vertices and 8 edges.

1103 is a number that cannot be written as a sum of three squares.

1103 is a prime whose reversal is a different prime: 3011.

The Intel 1103 DRAM, introduced in 1970, was the first chip to store a significant amount of information.

Source: Prime Curios!