Two partners performing oral sex and/or digital penetration on each other at the same time. Basically you have two people aligning themselves so that each person's mouth is near the other's genitals.

69 is often followed or preceded (in bed) by

and by

but very few people are keen to perform it after

A partner-in-bed of mine once told me that to prolong his resistance during sex and to avoid to ejaculate too fast he alternated focusing on the sexual act with focusing on math operations to keep his excitement at ease. I don't know if this would work with everybody, but since he is a good lover who lasts enough to please his female partner, i have decided to give you some information about the above numbers, if you would like to test his theory. Let me know if it works for you too.

69, 57 and 21 are non prime numbers. However if you sum them to the number two, like the number of the performers of the above positions, they become 71, 59 and 23 which are all prime numbers.

69. 57 and 21 are all divisible by 3.

**#69**

As well as 6 and 9 being the same digit rotated 180 degrees, they are also binary complements:

6 = 0110

9 = 1001

It is the Zodiac sign of the Cancer.

**#57**

is a 20-gonal number and it can also be expressed as a sum x^y+y^x, where x and y are integers greater than 1: 57=2^5+5^2.

Such numbers are called 'Leyland numbers'.

57 is the number of sauce varieties Henry J. Heinz lied about to promote his famous ketchup (when he began his business, he actually had many fewer than 57 sauces or food products!). The Heinz people are still quite attached to the number 57: the phone number at corporate headquarters in Pittsburgh is 237-5757, and the address is P.O. Box 57.

**#21**

is the number of spots on a standard cubical die (1+2+3+4+5+6).

It is also the smallest number with 5 representations as a sum of 3 primes:

21 = 2 + 2 + 17 = 3 + 5 + 13 = 3 + 7 + 11 = 5 + 5 + 11 = 7 + 7 + 7 .

21 is the fewest number of distinct integer-sided squares needed to tile a square. The simple perfect squared square shown below was discovered by A. J. W. Duijvestijn in 1976 - Journal of Combination Theory.

**#17**

It is a prime number.

17 and 19 form a twin prime pair.

It is the only prime number which is the sum of 4 consecutive primes:

17 = 2 + 3 + 5 + 7

It is also the smallest number with four representations as a sum of three primes:

17 = 2 + 2 + 13 = 3 + 3 + 11 = 3 + 7 + 7 = 5 + 5 + 7.

The multiplicative inverse of 17 gives a decimal expansion with a 16-digit repeating decimal:

1/17=0,05882352941176470588235294117647...

There are 17 ways to express 17 as the sum of one or more primes; 17 is the only integer that is equal to the number of prime partitions of itself.