21947561664 has 56 divisors (see below), whose sum is σ = 66365250048. Its totient is φ = 6270731520.

The previous prime is 21947561641. The next prime is 21947561681. The reversal of 21947561664 is 46616574912.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (56).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8163672 + ... + 8166359.

Almost surely, 2^21947561664 is an apocalyptic number.

21947561664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21947561664 is an abundant number, since it is smaller than the sum of its proper divisors (44417688384).

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

21947561664 is a wasteful number, since it uses less digits than its factorization.

21947561664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16330053 (or 16330043 counting only the distinct ones).

The product of its digits is 2177280, while the sum is 51.

The spelling of 21947561664 in words is "twenty-one billion, nine hundred forty-seven million, five hundred sixty-one thousand, six hundred sixty-four".