2009

2009 = 7² x 41.

2009 is an apocalyptic power because 2²⁰⁰⁹ contains the decimal digit string 666.

2009 has been designated the International Year of Astronomy, coinciding with the 400th anniversary of the first recorded astronomical observations with a telescope (Galileo Galilei) and the publication of Astronomia Nova (Johannes Kepler). The United Nations has also designated 2009 the International Year of Natural Fibres.

In the United States, 2009 is the Year of Science, presented by the Coalition on the Public Understanding of Science (COPUS).

Source: Number Gossip

17

17 is a prime number. It is the third Fermat prime: 17 = 2²^2 + 1.

Carl Friedrich Gauss proved at the age of 18 that one can construct a regular polygon with a prime number of sides with the use of only straight edge and compasses only if the number of sides is of the form 2²^n. Hence, one can construct a regular 17-gon with rule and compasses only.



17 is the first sum of two distinct fourth powers: 17 = 1⁴ + 2⁴.

There are 17 ways to express 17 as the sum of one or more primes; 17 is the only integer that is equal to the number of prime partitions of itself.

Source: Number Gossip

1717

1717 = 17 x 101

1717 is a pentagonal number.

French mathematician and encylopaedist Jean le Rond d'Alembert was born on Nov. 16, 1717.

Photo credit: MathDL Portrait Gallery

Source: Number Gossip

1233

1233 = 3² x 137

1233 is the smallest 2n-digit number that is the sum of the squares of its n-digit halves: 12² + 33² = 1233.


Source: Number Gossip

6141

6141 = 3 x 23 x 89

6141 is a Kaprekar constant in base 2. See http://mathworld.wolfram.com/KaprekarRoutine.html.


6141 Durda is a Mars-crossing asteroid discovered in 1992.

Source: JPL

1223

1223 is a prime number.

1223 is the smallest number with complexity 24. The complexity of an integer is the least number of 1s needed to represent it using only additions, multiplications, and parantheses.


Source: Wolfram MathWorld

866

866 = 2 x 433

866 is the smallest number n such that the sum of the proper divisors of n², excluding 1, is a square.


866 is one of the telephone area codes for toll-free calls.

Source: Number Gossip

738

738 = 2 x 3² x 41

738 = 6 + 66 + 666



The SVI 738 - Xpress was a home computer manufactured by Spectravideo in 1986.

Source: What Special About This Number?

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.


Source: Wolfram MathWorld

443

443 is the 24th Sophie Germain prime number: 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.

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.


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.


Source: Number Gossip

249

249 = 3 x 83

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.

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.


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

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).


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.



Check out "The Mystique of 47" at Pomona College, California.

Sources: Number Gossip; Prime Curios!

711

711 = 3² x 79

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.