21991836 has 12 divisors (see below), whose sum is σ = 51314312. Its totient is φ = 7330608.

The previous prime is 21991813. The next prime is 21991843. The reversal of 21991836 is 63819912.

It is a tau number, because it is divible by the number of its divisors (12).

It is a junction number, because it is equal to n+sod(n) for n = 21991794 and 21991803.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 916315 + ... + 916338.

Almost surely, 2^21991836 is an apocalyptic number.

It is an amenable number.

21991836 is an abundant number, since it is smaller than the sum of its proper divisors (29322476).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21991836 is a wasteful number, since it uses less digits than its factorization.

21991836 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1832660 (or 1832658 counting only the distinct ones).

The product of its digits is 23328, while the sum is 39.

The square root of 21991836 is about 4689.5453937455. The cubic root of 21991836 is about 280.1692683999.

The spelling of 21991836 in words is "twenty-one million, nine hundred ninety-one thousand, eight hundred thirty-six".