21781251765664 has 24 divisors (see below), whose sum is σ = 42882037974468. Its totient is φ = 10890575454720.

The previous prime is 21781251765649. The next prime is 21781251765703. The reversal of 21781251765664 is 46656715218712.

It can be written as a sum of positive squares in 2 ways, for example, as 19099871715600 + 2681380050064 = 4370340^2 + 1637492^2 .

It is a super-2 number, since 2×21781251765664² (a number of 27 digits) contains 22 as substring.

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, 6003804 + ... + 8922340.

Almost surely, 2^{21781251765664} is an apocalyptic number.

It is an amenable number.

21781251765664 is a deficient number, since it is larger than the sum of its proper divisors (21100786208804).

21781251765664 is a wasteful number, since it uses less digits than its factorization.

21781251765664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3151768 (or 3151760 counting only the distinct ones).

The product of its digits is 33868800, while the sum is 61.

The spelling of 21781251765664 in words is "twenty-one trillion, seven hundred eighty-one billion, two hundred fifty-one million, seven hundred sixty-five thousand, six hundred sixty-four".