21664875 has 16 divisors (see below), whose sum is σ = 36050976. Its totient is φ = 11554400.

The previous prime is 21664861. The next prime is 21664879. The reversal of 21664875 is 57846612.

It is not a de Polignac number, because 21664875 - 2¹³ = 21656683 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21664879) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28512 + ... + 29261.

It is an arithmetic number, because the mean of its divisors is an integer number (2253186).

Almost surely, 2^21664875 is an apocalyptic number.

21664875 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21664875 is a deficient number, since it is larger than the sum of its proper divisors (14386101).

21664875 is an equidigital number, since it uses as much as digits as its factorization.

21664875 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57791 (or 57781 counting only the distinct ones).

The product of its digits is 80640, while the sum is 39.

The square root of 21664875 is about 4654.5542214051. The cubic root of 21664875 is about 278.7738690038.

The spelling of 21664875 in words is "twenty-one million, six hundred sixty-four thousand, eight hundred seventy-five".