21365865 has 24 divisors (see below), whose sum is σ = 37147968. Its totient is φ = 11360160.

The previous prime is 21365849. The next prime is 21365887. The reversal of 21365865 is 56856312.

It is not a de Polignac number, because 21365865 - 2⁴ = 21365849 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 21612 + ... + 22578.

It is an arithmetic number, because the mean of its divisors is an integer number (1547832).

Almost surely, 2^21365865 is an apocalyptic number.

It is an amenable number.

21365865 is a deficient number, since it is larger than the sum of its proper divisors (15782103).

21365865 is a wasteful number, since it uses less digits than its factorization.

21365865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1469 (or 1466 counting only the distinct ones).

The product of its digits is 43200, while the sum is 36.

The square root of 21365865 is about 4622.3224681971. The cubic root of 21365865 is about 277.4854143783.

It can be divided in two parts, 2136 and 5865, that added together give a triangular number (8001 = T₁₂₆).

The spelling of 21365865 in words is "twenty-one million, three hundred sixty-five thousand, eight hundred sixty-five".