21521507660 has 24 divisors (see below), whose sum is σ = 45595128096. Its totient is φ = 8532419840.

The previous prime is 21521507647. The next prime is 21521507681. The reversal of 21521507660 is 6670512512.

It is a self number, because there is not a number n which added to its sum of digits gives 21521507660.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4759136 + ... + 4763655.

It is an arithmetic number, because the mean of its divisors is an integer number (1899797004).

Almost surely, 2^21521507660 is an apocalyptic number.

21521507660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21521507660 is an abundant number, since it is smaller than the sum of its proper divisors (24073620436).

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

21521507660 is a wasteful number, since it uses less digits than its factorization.

21521507660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9522913 (or 9522911 counting only the distinct ones).

The product of its (nonzero) digits is 25200, while the sum is 35.

The spelling of 21521507660 in words is "twenty-one billion, five hundred twenty-one million, five hundred seven thousand, six hundred sixty".