69 (sixty-nine) is the natural number following 68 and preceding 70.

In mathematics

69 is:

• a lucky number.^[1]
• the twentieth semiprime (3.23)^[2] and the seventh of the form (3.q) where q is a higher prime.^[3]
• the aliquot sum of sixty-nine is 27 within the aliquot sequence (69,27,13,1,0) and is the third composite number in the 13-aliquot tree; following (27,35).
• a Blum integer, since the two factors of 69 are both Gaussian primes.^[4]
• the sum of the sums of the divisors of the first 9 positive integers.^[5]
• a strobogrammatic number.^[6]
• a centered tetrahedral number.

Because 69 has an odd number of 1s in its binary representation, it is sometimes called an "odious number."

In decimal, 69 is the only natural number whose square (4761) and cube (328509) use every digit from 0–9 exactly once.^[7]

69 is equal to 105 octal, while 105 is equal to 69 hexadecimal. This same property can be applied to all numbers from 64 to 69.

On many handheld scientific and graphing calculators, the highest factorial that can be calculated, due to memory limitations, is 69!, or about 1.711224524×10⁹⁸.

In science

• The atomic number of thulium, a lanthanide.

Astronomy

• The Messier object M69 is a magnitude 9.0 globular cluster in the constellation Sagittarius.

In other fields

Sixty-nine may also refer to:

• 69ing, a sex position involving each partner aligning themselves to achieve oral sex simultaneously with each other.
  • In reference to the sex position, "69" has become an Internet meme, where users will respond to any occurrence of the number with the word "nice" to draw specific attention to it. This means to humorously imply that the reference to the sex position was intentional. Because of its association with the sex position and resulting meme, "69" has been named "the sex number".^[8]
• The registry of the U.S. Navy's aircraft carrier USS Dwight D. Eisenhower (CVN-69), named after Dwight D. Eisenhower, the 34th President of the United States and five-star general in the United States Army.
• The number of the French department Rhône. The Lyon Metropolis, which was separated from the Rhône department in 2015, is designated as "69M". The postal codes for both entities start with "69".
• The Taijitu
• The last possible television channel number in the UHF bandplan for American terrestrial television from 1982 until its withdrawal on December 31, 2011.