21265520 has 20 divisors (see below), whose sum is σ = 49442520. Its totient is φ = 8506176.

The previous prime is 21265459. The next prime is 21265523. The reversal of 21265520 is 2556212.

It is a tau number, because it is divible by the number of its divisors (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21265523) 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 3 ways as a sum of consecutive naturals, for example, 132830 + ... + 132989.

It is an arithmetic number, because the mean of its divisors is an integer number (2472126).

Almost surely, 2^21265520 is an apocalyptic number.

21265520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21265520 is an abundant number, since it is smaller than the sum of its proper divisors (28177000).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21265520 is a wasteful number, since it uses less digits than its factorization.

21265520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 265832 (or 265826 counting only the distinct ones).

The product of its (nonzero) digits is 1200, while the sum is 23.

The square root of 21265520 is about 4611.4553017459. The cubic root of 21265520 is about 277.0503281897.

The spelling of 21265520 in words is "twenty-one million, two hundred sixty-five thousand, five hundred twenty".