21257665 has 24 divisors (see below), whose sum is σ = 30146688. Its totient is φ = 14264640.

The previous prime is 21257651. The next prime is 21257669. The reversal of 21257665 is 56675212.

It is not a de Polignac number, because 21257665 - 2²³ = 12869057 is a prime.

It is a Smith number, since the sum of its digits (34) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 21257665.

It is not an unprimeable number, because it can be changed into a prime (21257669) 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, 8152 + ... + 10438.

It is an arithmetic number, because the mean of its divisors is an integer number (1256112).

Almost surely, 2^21257665 is an apocalyptic number.

It is an amenable number.

21257665 is a deficient number, since it is larger than the sum of its proper divisors (8889023).

21257665 is a wasteful number, since it uses less digits than its factorization.

21257665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2329 (or 2316 counting only the distinct ones).

The product of its digits is 25200, while the sum is 34.

The square root of 21257665 is about 4610.6035396681. The cubic root of 21257665 is about 277.0162119563.

The spelling of 21257665 in words is "twenty-one million, two hundred fifty-seven thousand, six hundred sixty-five".