4

is the integer between and.

Math features

 * 4 is the first composite number.
 * 4 is equal to 2+2, 2×2, $$2^2$$, $$^22$$, 2↑↑↑2, 2↑↑↑↑2, and so on. In general, 4 = 2↑↑↑...↑↑2, where there is a integer number of ↑s.
 * 4 is the first even natural square number.
 * 4 is a power of 2.
 * 4 is a square highly composite number.
 * 4 is one of the only two powers of 2 that are highly composite.