21561326656 has 28 divisors (see below), whose sum is σ = 43829317980. Its totient is φ = 10517719040.

The previous prime is 21561326653. The next prime is 21561326669. The reversal of 21561326656 is 65662316512.

It can be written as a sum of positive squares in 2 ways, for example, as 4567597056 + 16993729600 = 67584^2 + 130360^2 .

It is a super-2 number, since 2×21561326656² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21561326651) 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, 4105861 + ... + 4111108.

It is an arithmetic number, because the mean of its divisors is an integer number (1565332785).

Almost surely, 2^21561326656 is an apocalyptic number.

It is an amenable number.

21561326656 is an abundant number, since it is smaller than the sum of its proper divisors (22267991324).

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

21561326656 is an equidigital number, since it uses as much as digits as its factorization.

21561326656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8217022 (or 8217012 counting only the distinct ones).

The product of its digits is 388800, while the sum is 43.

The spelling of 21561326656 in words is "twenty-one billion, five hundred sixty-one million, three hundred twenty-six thousand, six hundred fifty-six".