21561712775 has 12 divisors (see below), whose sum is σ = 26746335000. Its totient is φ = 17243040480.

The previous prime is 21561712771. The next prime is 21561712789. The reversal of 21561712775 is 57721716512.

It is not a de Polignac number, because 21561712775 - 2² = 21561712771 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561712771) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 88145 + ... + 225594.

It is an arithmetic number, because the mean of its divisors is an integer number (2228861250).

Almost surely, 2^21561712775 is an apocalyptic number.

21561712775 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21561712775 is a deficient number, since it is larger than the sum of its proper divisors (5184622225).

21561712775 is a wasteful number, since it uses less digits than its factorization.

21561712775 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 316498 (or 316493 counting only the distinct ones).

The product of its digits is 205800, while the sum is 44.

The spelling of 21561712775 in words is "twenty-one billion, five hundred sixty-one million, seven hundred twelve thousand, seven hundred seventy-five".