21561036751 has 6 divisors (see below), whose sum is σ = 22159518360. Its totient is φ = 20978304696.

The previous prime is 21561036697. The next prime is 21561036767. The reversal of 21561036751 is 15763016512.

It is a de Polignac number, because none of the positive numbers 2^k-21561036751 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21561036751.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561036451) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 7873371 + ... + 7876108.

It is an arithmetic number, because the mean of its divisors is an integer number (3693253060).

Almost surely, 2^21561036751 is an apocalyptic number.

21561036751 is a deficient number, since it is larger than the sum of its proper divisors (598481609).

21561036751 is an equidigital number, since it uses as much as digits as its factorization.

21561036751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15749553 (or 15749516 counting only the distinct ones).

The product of its (nonzero) digits is 37800, while the sum is 37.

The spelling of 21561036751 in words is "twenty-one billion, five hundred sixty-one million, thirty-six thousand, seven hundred fifty-one".