21565825 has 6 divisors (see below), whose sum is σ = 26741654. Its totient is φ = 17252640.

The previous prime is 21565811. The next prime is 21565837. The reversal of 21565825 is 52856512.

It can be written as a sum of positive squares in 3 ways, for example, as 2241009 + 19324816 = 1497^2 + 4396^2 .

It is not a de Polignac number, because 21565825 - 2¹¹ = 21563777 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 431292 + ... + 431341.

Almost surely, 2^21565825 is an apocalyptic number.

21565825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21565825 is a deficient number, since it is larger than the sum of its proper divisors (5175829).

21565825 is an equidigital number, since it uses as much as digits as its factorization.

21565825 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 862643 (or 862638 counting only the distinct ones).

The product of its digits is 24000, while the sum is 34.

The square root of 21565825 is about 4643.9019154155. The cubic root of 21565825 is about 278.3483762851.

The spelling of 21565825 in words is "twenty-one million, five hundred sixty-five thousand, eight hundred twenty-five".