21165265 has 16 divisors (see below), whose sum is σ = 27812160. Its totient is φ = 15334720.

The previous prime is 21165251. The next prime is 21165271. The reversal of 21165265 is 56256112.

It is not a de Polignac number, because 21165265 - 2¹⁵ = 21132497 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18531 + ... + 19639.

It is an arithmetic number, because the mean of its divisors is an integer number (1738260).

Almost surely, 2^21165265 is an apocalyptic number.

It is an amenable number.

21165265 is a deficient number, since it is larger than the sum of its proper divisors (6646895).

21165265 is a wasteful number, since it uses less digits than its factorization.

21165265 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1472.

The product of its digits is 3600, while the sum is 28.

The square root of 21165265 is about 4600.5722470145. The cubic root of 21165265 is about 276.6142632318.

It can be divided in two parts, 2116 and 5265, that added together give a triangular number (7381 = T₁₂₁).

The spelling of 21165265 in words is "twenty-one million, one hundred sixty-five thousand, two hundred sixty-five".