21523865 has 32 divisors (see below), whose sum is σ = 30412800. Its totient is φ = 14454720.

The previous prime is 21523847. The next prime is 21523891. The reversal of 21523865 is 56832512.

It is not a de Polignac number, because 21523865 - 2⁸ = 21523609 is a prime.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 44696 + ... + 45174.

It is an arithmetic number, because the mean of its divisors is an integer number (950400).

Almost surely, 2^21523865 is an apocalyptic number.

It is an amenable number.

21523865 is a deficient number, since it is larger than the sum of its proper divisors (8888935).

21523865 is a wasteful number, since it uses less digits than its factorization.

21523865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 557.

The product of its digits is 14400, while the sum is 32.

The square root of 21523865 is about 4639.3819631498. The cubic root of 21523865 is about 278.1677342911.

The spelling of 21523865 in words is "twenty-one million, five hundred twenty-three thousand, eight hundred sixty-five".