21212520 has 64 divisors (see below), whose sum is σ = 72731520. Its totient is φ = 4848384.

The previous prime is 21212519. The next prime is 21212537. The reversal of 21212520 is 2521212.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21212520.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11787 + ... + 13466.

It is an arithmetic number, because the mean of its divisors is an integer number (1136430).

Almost surely, 2^21212520 is an apocalyptic number.

21212520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21212520 is an abundant number, since it is smaller than the sum of its proper divisors (51519000).

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

21212520 is a wasteful number, since it uses less digits than its factorization.

21212520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25274 (or 25270 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21212520 is about 4605.7051577364. The cubic root of 21212520 is about 276.8199727756.

Adding to 21212520 its reverse (2521212), we get a palindrome (23733732).

The spelling of 21212520 in words is "twenty-one million, two hundred twelve thousand, five hundred twenty".