21561638373 has 96 divisors (see below), whose sum is σ = 37344827520. Its totient is φ = 12151365120.

The previous prime is 21561638363. The next prime is 21561638419. The reversal of 21561638373 is 37383616512.

21561638373 is a `hidden beast` number, since 2 + 1 + 5 + 6 + 1 + 638 + 3 + 7 + 3 = 666.

It is not a de Polignac number, because 21561638373 - 2⁶ = 21561638309 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561638363) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 57805815 + ... + 57806187.

It is an arithmetic number, because the mean of its divisors is an integer number (389008620).

Almost surely, 2^21561638373 is an apocalyptic number.

It is an amenable number.

21561638373 is a deficient number, since it is larger than the sum of its proper divisors (15783189147).

21561638373 is a wasteful number, since it uses less digits than its factorization.

21561638373 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 624 (or 511 counting only the distinct ones).

The product of its digits is 544320, while the sum is 45.

The spelling of 21561638373 in words is "twenty-one billion, five hundred sixty-one million, six hundred thirty-eight thousand, three hundred seventy-three".