655

655 = 5 x 131.

655 is a semiprime (product of two prime numbers) that is the product of two Sophie Germain primes, 5 and 131.

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

655 is a divisor of 61⁵ - 1.

655 is 22033 in base 4 and 10110 in base 5.

Iran Air Flight 655 was an airliner shot down by U.S. missiles in 1988 toward the end of the Iran-Iraq war.

Source: On-Line Encyclopedia of Integer Sequences

223

223 is a prime number.

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

223 is the smallest prime with three prime digits. The sum of the digits of first primes up to 223 is 449.

223 is the smallest prime whose reversal has more than two prime divisors: 322 = 2 x 7 x 23.

223 is the final chapter of Mark Haddon's novel The Curious Incident of the Dog in the Night-Time, which uses just prime numbers for its chapters.

Source: Number Gossip

642

642 = 2 x 3 x 107.

642 is a sphenic number because it the product of three distinct primes.

642 is the smallest number with the property that its first six multiples contain the digit 2: 642, 1284, 1926, 2568, 3210, 3852.

642 is 22002 in base 4, 1202 in base 8, and 456 in base 12.

642 Clara is an asteroid orbiting the Sun.

Source: What's Special About This Number?

426

426 = 2 x 3 x 71.

As the product of three distinct primes, 426 is known as a sphenic number.

426 is a stella octangula number. The stella octangula is a stellation of the octahedron.

426 is a number such that 10⁴²⁶ + 3 is a prime.

426 is a multiple of 6 that contains 6 in its decimal representation.

In the 1979 movie Alien, the spaceship Nostromo goes to the desolate planetoid LV-426.

Source: What's Special About This Number?

808

808 = 2³ x 101.

808 has a representation as a sum of two squares: 808 = 18² + 22².

The first 808 digits of 808! form a prime number.

808 is a strobogrammatic number. It is the same number when rotated 180 degrees on an axis perpendicular to the plane on which the number is written.

The 808th Fibonacci number plus and minus 808 results in (13²)-digit primes.

The Roland TR-808 was one of the first programmable drum machines, introduced in early 1980.

Source: Prime Curios!

314

314 = 2 x 157.

314 has a representation as a sum of two squares: 314 = 5² + 17².

314 is the smallest number that can be written as the sum of three positive squares in six ways: 314 = 17² + 4² + 3² = 16² + 7² + 3² = 15² + 8² + 5² = 13² + 9² + 8² = 13² + 12² + 1² = 13² + 9² + 8².

314 is 222 in base 12.

314 is the only number that together with its sixth power, 958468597212736, has each digit from 1 to 9 occurring exactly twice.

314 is the telephone area code for St. Louis, Missouri.

Source: Number Gossip

2265

2265 = 3 x 5 x 151. It has exactly three distinct palindromic prime factors.

The sum of the digits of 2265 equals the sum of the digits of its prime factors: 2 + 2 + 6 + 5 = 3 + 5 + 1 + 5 + 1 = 15.

The product of the digits of 2265 is eight times the sum of the digits: 2 x 2 x 6 x 5 = 8(2 + 2 + 6 + 5) = 120.

2265 is 14253 in base 6. It uses each positive digit just once.

2265 is a year in which January 1 falls on a Sunday.

Source: On-Line Encyclopedia of Integer Sequences.

3531

3531 = 3 x 11 x 107.

3531 is a composite number whose three prime factors are distinct in length.

3531 is 24203 in base 6 and 13203 in base 7.

3531 is a multiple of 11 having only odd digits.

3531 is the number of sums payable using exactly 39 banknotes of denominations 1, 5, 10, 20, 50, and 100. For n = 1, there are precisely six payable sums.

The Lego 3531 set was a kit for building the Znap Tri-bike.

Source: On-Line Encyclopedia of Integer Sequences

9002

9002 = 2 x 7 x 643.

9002 = 3² x 10³ + 2.

9002 is a value of n such that n + 7 and n(n + 7) are palindromes: 9009 and 81099018.

9002 is a number n such that n(n + 7) is a palindrome: 9002(9009) = 81099018.

ISO 9002 was an international standard to used to certify manufacturing quality.

Source: What's Special About This Number?

774

774 = 2 x 3² x 43.

774 is 3330 in base 6 and 1050 in base 9.

The sum of the digits of 774 is six times the number of digits: 7 + 7 + 4 = 18 = 6 x 3.

774 is the sum of twelve positive fifth powers: 744 = 3⁵ + 3⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 1⁵ + 1⁵.

774 Armor is an asteroid orbiting the Sun.

Source: On-Line Encyclopedia of Integer Sequences

986

986 = 2 x 17 x 29.

986 has two representations as a sum of two squares: 986 = 5² + 31² = 19² + 25².

986 is a strobogrammatic number. It is a number that is the same whether it is viewed normally or upside down.

986 = 1⁹ + 2⁸ + 3⁶.

986 is 12421 in base 5.

NGC 986 is a galaxy in the constellation Fornax.

Source: What's Special About This Number?

803

803 = 11 x 73.

803 is the sum of three consecutive prime numbers: 803 = 263 + 269 + 271. It is also the sum of nine consecutive primes: 803 = 71 + 73 + 79 + 83 + 89 + 97 + 101 + 103 + 107.

803 is 30203 in base 4, 323 in base 16, and 203 in base 20.

803 is a divisor of 99999999.

Telephone area code 803 covers southern South Carolina.

Source: On-Line Encyclopedia of Integer Sequences

593

593 is a prime number. It is a Sophie Germain prime because 2 x 593 + 1 = 1187 is also prime.

593 has a representation as a sum of two squares: 593 = 8² + 23².

593 is the hypotenuse of a primitive Pythagorean triple: 593² = 368² + 465².

593 = 9² + 2⁹ = 3^2*2 + 2^3*3.

593 is the number on the conning tower of the submarine USS Wayne in the movie The Spy Who Loved Me.

Source: Prime Curios!

388

388 = 2² x 97.

388 has a representation as a sum of two squares: 388 = 8² + 18².

The number 388 followed by 388 sevens is a prime number.

388 is the maximum value of n so that there exist 6 denominations of stamps so that every postage from 1 to n can be paid for with at most 6 stamps.

The Junkers Ju 388 was a German World War II aircraft.

Source: Prime Curios!

531

531 = 3² x 59.

531 is the smallest number with the property that its first four multiples contain the digit 1: 531, 1062, 1593, and 2124.

291,548,736 = 8 x 92 x 531 x 746. Both the number and its factors use each of the digits from 1 to 9 exactly once.

531 is 20103 in base 4 and 213 in base 16.

The construction of the St. Sophia Basilica in Constantinople began in the year 531.

Source: What's Special About This Number?

623

623 = 7 x 89.

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

623 - 6*2*3 and 623 + 6*2*3 are prime numbers: 587 and 659.

623 is the sum of three distinct positive cubes: 623 = 4³ + 6³ + 7³.

A Uranus-Neptune conjunction in Virgo occurred in the year 623.

Source: Prime Curios!

205

205 = 5 x 41.

205 has two representations as a sum of two squares: 205 = 3² + 14² = 6² + 13².

205 is the hypotenuse of two primitive Pythagorean triples: 205² = 84² + 187² = 133² + 156².

Every number greater than 205 is the sum of distinct primes of the form 6n + 1.

205 is the number of pairs of twin primes less than 10,000.

The Peugeot 205 is a supermini produced by the French car manufacturer Peugeot between 1983 and 1997.

Source: Prime Curios!