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169 (one hundred 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 ${\displaystyle 8^{3}-7^{3}.}$

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

1. "Sloane's A003215 : Hex (or centered hexagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-28.

External links

• Number Facts and Trivia: 169
• The Positive Integer 169
• Prime curiosities: 169
• The Number 169
• Number Gossip 169

• Integers