21993808 has 10 divisors (see below), whose sum is σ = 42613034. Its totient is φ = 10996896.

The previous prime is 21993793. The next prime is 21993809. The reversal of 21993808 is 80839912.

It can be written as a sum of positive squares in only one way, i.e., 12334144 + 9659664 = 3512^2 + 3108^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21993809) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 687291 + ... + 687322.

Almost surely, 2^21993808 is an apocalyptic number.

It is an amenable number.

21993808 is a deficient number, since it is larger than the sum of its proper divisors (20619226).

21993808 is a wasteful number, since it uses less digits than its factorization.

21993808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1374621 (or 1374615 counting only the distinct ones).

The product of its (nonzero) digits is 31104, while the sum is 40.

The square root of 21993808 is about 4689.7556439542. The cubic root of 21993808 is about 280.1776423753.

It can be divided in two parts, 21993 and 808, that added together give a square (22801 = 151²).

The spelling of 21993808 in words is "twenty-one million, nine hundred ninety-three thousand, eight hundred eight".