21215925 has 30 divisors (see below), whose sum is σ = 39302978. Its totient is φ = 11314080.

The previous prime is 21215921. The next prime is 21215939. The reversal of 21215925 is 52951212.

It can be written as a sum of positive squares in 3 ways, for example, as 3017169 + 18198756 = 1737^2 + 4266^2 .

It is not a de Polignac number, because 21215925 - 2² = 21215921 is a prime.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21215921) by changing a digit.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 3214 + ... + 7263.

Almost surely, 2^21215925 is an apocalyptic number.

21215925 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21215925 is a deficient number, since it is larger than the sum of its proper divisors (18087053).

21215925 is a wasteful number, since it uses less digits than its factorization.

21215925 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10499 (or 10485 counting only the distinct ones).

The product of its digits is 1800, while the sum is 27.

The square root of 21215925 is about 4606.0747931400. The cubic root of 21215925 is about 276.8347835505.

The spelling of 21215925 in words is "twenty-one million, two hundred fifteen thousand, nine hundred twenty-five".