169 (number)

169 (one hundred [and] sixty-nine) is the natural number following 168 and preceding 170. == In mathematics == 169 is an odd number, a composite number, and a deficient number. 169 is a square number: 13 × 13 = 169, and if each number is reversed the equation is still true: 31 × 31 = 961. 144 shares this property: 12 × 12 = 144, 21 × 21 = 441. 169 is one of the few squares to also be a centered hexagonal number. Like all odd squares, it is a centered octagonal number. 169 is an odd-indexed Pell number, thus it is also a Markov number, appearing in the solutions (2, 169, 985), (2, 29, 169), (29, 169, 14701), etc. 169 is the sum of seven consecutive primes: 13 + 17 + 19 + 23 + 29 + 31 + 37. 169 is a difference in consecutive cubes, equaling 8 3 − 7 3 . {\displaystyle 8^{3}-7^{3}.} == In other fields == 169 is known in the computing world as the first number of an automatic IPv4 address assigned by TCP/IP when no external networking device is contactable. == References == == External links == Number Facts and Trivia: 169 The Positive Integer 169 Prime curiosities: 169 The Number 169 Number Gossip 169