21156720500 has 24 divisors (see below), whose sum is σ = 46206278664. Its totient is φ = 8462688000.

The previous prime is 21156720491. The next prime is 21156720521. The reversal of 21156720500 is 502765112.

It can be written as a sum of positive squares in 4 ways, for example, as 66129424 + 21090591076 = 8132^2 + 145226^2 .

It is a hoax number, since the sum of its digits (29) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

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, 21156221 + ... + 21157220.

It is an arithmetic number, because the mean of its divisors is an integer number (1925261611).

Almost surely, 2^21156720500 is an apocalyptic number.

21156720500 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21156720500 is an abundant number, since it is smaller than the sum of its proper divisors (25049558164).

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

21156720500 is a wasteful number, since it uses less digits than its factorization.

21156720500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42313460 (or 42313448 counting only the distinct ones).

The product of its (nonzero) digits is 4200, while the sum is 29.

The spelling of 21156720500 in words is "twenty-one billion, one hundred fifty-six million, seven hundred twenty thousand, five hundred".