21657316561 has 4 divisors (see below), whose sum is σ = 21665677824. Its totient is φ = 21648955300.

The previous prime is 21657316519. The next prime is 21657316567. The reversal of 21657316561 is 16561375612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21657316561 - 2¹¹ = 21657314513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21657316567) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4176745 + ... + 4181926.

It is an arithmetic number, because the mean of its divisors is an integer number (5416419456).

Almost surely, 2^21657316561 is an apocalyptic number.

It is an amenable number.

21657316561 is a deficient number, since it is larger than the sum of its proper divisors (8361263).

21657316561 is an equidigital number, since it uses as much as digits as its factorization.

21657316561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8361262.

The product of its digits is 226800, while the sum is 43.

The spelling of 21657316561 in words is "twenty-one billion, six hundred fifty-seven million, three hundred sixteen thousand, five hundred sixty-one".