21656021660 has 72 divisors (see below), whose sum is σ = 56280089376. Its totient is φ = 6853766400.

The previous prime is 21656021627. The next prime is 21656021669. The reversal of 21656021660 is 6612065612.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a self number, because there is not a number n which added to its sum of digits gives 21656021660.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21656021669) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 433991 + ... + 481310.

It is an arithmetic number, because the mean of its divisors is an integer number (781667908).

Almost surely, 2^21656021660 is an apocalyptic number.

21656021660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21656021660 is an abundant number, since it is smaller than the sum of its proper divisors (34624067716).

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

21656021660 is a wasteful number, since it uses less digits than its factorization.

21656021660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 915343 (or 915328 counting only the distinct ones).

The product of its (nonzero) digits is 25920, while the sum is 35.

The spelling of 21656021660 in words is "twenty-one billion, six hundred fifty-six million, twenty-one thousand, six hundred sixty".