21520644 has 12 divisors (see below), whose sum is σ = 50214864. Its totient is φ = 7173544.

The previous prime is 21520637. The next prime is 21520649. The reversal of 21520644 is 44602512.

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

It is not an unprimeable number, because it can be changed into a prime (21520649) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 896682 + ... + 896705.

It is an arithmetic number, because the mean of its divisors is an integer number (4184572).

Almost surely, 2^21520644 is an apocalyptic number.

It is an amenable number.

21520644 is an abundant number, since it is smaller than the sum of its proper divisors (28694220).

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

21520644 is a wasteful number, since it uses less digits than its factorization.

21520644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1793394 (or 1793392 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 24.

The square root of 21520644 is about 4639.0348134068. The cubic root of 21520644 is about 278.1538578650.

The spelling of 21520644 in words is "twenty-one million, five hundred twenty thousand, six hundred forty-four".