>>5002316, >>5002333 (lb)

In mathematics:

22 is a deficient number.

22 is an even composite number and a semiprime; its proper divisors are 1, 2, and 11.

22 is a pentagonal number[1] and a centered heptagonal number.

When cutting a circle with just six line segments, the maximum number of pieces that can be so created is 22,[3] thus 22 is a central polygonal number (see lazy caterer's sequence).

22 is the sum of the totient function for the first eight integers.

22 is a Perrin number, preceded in the sequence by 10, 12, and 17.

22 divided by 7 approximates the irrational number π, the ratio of the circumference of a circle to its diameter.

22 is an Erdős–Woods number, since it is possible to find sequences of 22 consecutive integers such that each inner member shares a factor with either the first or the last member.

22 is a Smith number in base 10.

"2-2" is the only fixed point of John Conway's look-and-say function.

In physics and chemistry

22 is the atomic number of titanium.

In aircraft:

22 is the designation of the USAF stealth fighter, the F-22 Raptor.