21312520 has 32 divisors (see below), whose sum is σ = 49072320. Its totient is φ = 8326080.

The previous prime is 21312517. The next prime is 21312523. The reversal of 21312520 is 2521312.

It is an interprime number because it is at equal distance from previous prime (21312517) and next prime (21312523).

It is a junction number, because it is equal to n+sod(n) for n = 21312494 and 21312503.

It is not an unprimeable number, because it can be changed into a prime (21312523) 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, 4476 + ... + 7915.

It is an arithmetic number, because the mean of its divisors is an integer number (1533510).

Almost surely, 2^21312520 is an apocalyptic number.

21312520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21312520 is an abundant number, since it is smaller than the sum of its proper divisors (27759800).

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

21312520 is a wasteful number, since it uses less digits than its factorization.

21312520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12445 (or 12441 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21312520 is about 4616.5484942758. The cubic root of 21312520 is about 277.2542856465.

Adding to 21312520 its reverse (2521312), we get a palindrome (23833832).

The spelling of 21312520 in words is "twenty-one million, three hundred twelve thousand, five hundred twenty".