21657000020 has 12 divisors (see below), whose sum is σ = 45479700084. Its totient is φ = 8662800000.

The previous prime is 21656999981. The next prime is 21657000047. The reversal of 21657000020 is 2000075612.

It can be written as a sum of positive squares in 2 ways, for example, as 15844767376 + 5812232644 = 125876^2 + 76238^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21657000020.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 541424981 + ... + 541425020.

It is an arithmetic number, because the mean of its divisors is an integer number (3789975007).

Almost surely, 2^21657000020 is an apocalyptic number.

21657000020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21657000020 is an abundant number, since it is smaller than the sum of its proper divisors (23822700064).

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

21657000020 is a wasteful number, since it uses less digits than its factorization.

21657000020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1082850010 (or 1082850008 counting only the distinct ones).

The product of its (nonzero) digits is 840, while the sum is 23.

Adding to 21657000020 its reverse (2000075612), we get a palindrome (23657075632).

The spelling of 21657000020 in words is "twenty-one billion, six hundred fifty-seven million, twenty", and thus it is an aban number.