21915621 has 24 divisors (see below), whose sum is σ = 38962560. Its totient is φ = 11559456.

The previous prime is 21915617. The next prime is 21915629. The reversal of 21915621 is 12651912.

21915621 is a `hidden beast` number, since 21 + 9 + 15 + 621 = 666.

It is not a de Polignac number, because 21915621 - 2² = 21915617 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21915629) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 12561 + ... + 14198.

It is an arithmetic number, because the mean of its divisors is an integer number (1623440).

Almost surely, 2^21915621 is an apocalyptic number.

21915621 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21915621 is a deficient number, since it is larger than the sum of its proper divisors (17046939).

21915621 is a wasteful number, since it uses less digits than its factorization.

21915621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26785 (or 26782 counting only the distinct ones).

The product of its digits is 1080, while the sum is 27.

The square root of 21915621 is about 4681.4122869066. The cubic root of 21915621 is about 279.8452418607.

The spelling of 21915621 in words is "twenty-one million, nine hundred fifteen thousand, six hundred twenty-one".