21564775 has 12 divisors (see below), whose sum is σ = 27310752. Its totient is φ = 16883840.

The previous prime is 21564757. The next prime is 21564779. The reversal of 21564775 is 57746512.

It is not a de Polignac number, because 21564775 - 2⁵ = 21564743 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21564779) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 8002 + ... + 10351.

It is an arithmetic number, because the mean of its divisors is an integer number (2275896).

Almost surely, 2^21564775 is an apocalyptic number.

21564775 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21564775 is a deficient number, since it is larger than the sum of its proper divisors (5745977).

21564775 is a wasteful number, since it uses less digits than its factorization.

21564775 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18410 (or 18405 counting only the distinct ones).

The product of its digits is 58800, while the sum is 37.

The square root of 21564775 is about 4643.7888625561. The cubic root of 21564775 is about 278.3438587898.

The spelling of 21564775 in words is "twenty-one million, five hundred sixty-four thousand, seven hundred seventy-five".