21663625 has 8 divisors (see below), whose sum is σ = 27036360. Its totient is φ = 17330800.

The previous prime is 21663623. The next prime is 21663647. The reversal of 21663625 is 52636612.

It can be written as a sum of positive squares in 4 ways, for example, as 3370896 + 18292729 = 1836^2 + 4277^2 .

It is not a de Polignac number, because 21663625 - 2¹ = 21663623 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21663623) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 86530 + ... + 86779.

It is an arithmetic number, because the mean of its divisors is an integer number (3379545).

Almost surely, 2^21663625 is an apocalyptic number.

21663625 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21663625 is a deficient number, since it is larger than the sum of its proper divisors (5372735).

21663625 is an equidigital number, since it uses as much as digits as its factorization.

21663625 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 173324 (or 173314 counting only the distinct ones).

The product of its digits is 12960, while the sum is 31.

The square root of 21663625 is about 4654.4199423774. The cubic root of 21663625 is about 278.7685074214.

The spelling of 21663625 in words is "twenty-one million, six hundred sixty-three thousand, six hundred twenty-five".