21105665556 has 12 divisors (see below), whose sum is σ = 49246552992. Its totient is φ = 7035221848.

The previous prime is 21105665527. The next prime is 21105665573. The reversal of 21105665556 is 65556650112.

It is a tau number, because it is divible by the number of its divisors (12).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 879402720 + ... + 879402743.

It is an arithmetic number, because the mean of its divisors is an integer number (4103879416).

Almost surely, 2^21105665556 is an apocalyptic number.

It is an amenable number.

21105665556 is an abundant number, since it is smaller than the sum of its proper divisors (28140887436).

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

21105665556 is a wasteful number, since it uses less digits than its factorization.

21105665556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1758805470 (or 1758805468 counting only the distinct ones).

The product of its (nonzero) digits is 270000, while the sum is 42.

The spelling of 21105665556 in words is "twenty-one billion, one hundred five million, six hundred sixty-five thousand, five hundred fifty-six".