21265815 has 16 divisors (see below), whose sum is σ = 34126848. Its totient is φ = 11307936.

The previous prime is 21265789. The next prime is 21265817. The reversal of 21265815 is 51856212.

It is not a de Polignac number, because 21265815 - 2⁷ = 21265687 is a prime.

It is a super-2 number, since 2×21265815² = 904469775228450, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21265817) 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, 3574 + ... + 7436.

It is an arithmetic number, because the mean of its divisors is an integer number (2132928).

Almost surely, 2^21265815 is an apocalyptic number.

21265815 is a deficient number, since it is larger than the sum of its proper divisors (12861033).

21265815 is a wasteful number, since it uses less digits than its factorization.

21265815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4238.

The product of its digits is 4800, while the sum is 30.

The square root of 21265815 is about 4611.4872871992. The cubic root of 21265815 is about 277.0516092850.

The spelling of 21265815 in words is "twenty-one million, two hundred sixty-five thousand, eight hundred fifteen".