Chapter 69

In mathematics

69 is:

• a lucky number.

• a semiprime.

• a Blum integer, since the two factors of 69 are both Gaussian primes.

• the sum of the sums of the divisors of the first 9 positive integers.

• the third composite number in the 13-aliquot tree. The aliquot sum of sixty-nine is 27 within the aliquot sequence (69,27,13,1,0).

Because 69 has an odd number of 1s in its binary representation, it is sometimes called an "odious number." Of note is that 692 (4761) and 693 (328509) together use every decimal digit from 0-9. 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:

• The sex position, a sex position involving each partner aligning themselves to achieve oral sex simultaneously at each other.

• 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 number that fictional characters Bill Preston and Ted Logan were thinking of when talking to their future selves; see Bill & Ted's Excellent Adventure

• The last possible television channel number in the UHF bandplan for American terrestrial television from 1982 until its withdrawal on December 31, 2011