21165825 has 24 divisors (see below), whose sum is σ = 35169376. Its totient is φ = 11232000.

The previous prime is 21165817. The next prime is 21165827. The reversal of 21165825 is 52856112.

It is not a de Polignac number, because 21165825 - 2³ = 21165817 is a prime.

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21165792 and 21165801.

It is not an unprimeable number, because it can be changed into a prime (21165827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 17490 + ... + 18660.

Almost surely, 2^21165825 is an apocalyptic number.

21165825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21165825 is a deficient number, since it is larger than the sum of its proper divisors (14003551).

21165825 is a wasteful number, since it uses less digits than its factorization.

21165825 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1425 (or 1420 counting only the distinct ones).

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

The square root of 21165825 is about 4600.6331086058. The cubic root of 21165825 is about 276.6167028047.

The spelling of 21165825 in words is "twenty-one million, one hundred sixty-five thousand, eight hundred twenty-five".