21156817986 has 48 divisors (see below), whose sum is σ = 46281590784. Its totient is φ = 6984496512.

The previous prime is 21156817939. The next prime is 21156818027. The reversal of 21156817986 is 68971865112.

It is a happy number.

21156817986 is a `hidden beast` number, since 2 + 1 + 1 + 568 + 1 + 79 + 8 + 6 = 666.

It is a super-2 number, since 2×21156817986² (a number of 21 digits) contains 22 as substring.

It is a Smith number, since the sum of its digits (54) coincides with the sum of the digits of its prime factors.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1347795 + ... + 1363401.

It is an arithmetic number, because the mean of its divisors is an integer number (964199808).

Almost surely, 2^21156817986 is an apocalyptic number.

21156817986 is an abundant number, since it is smaller than the sum of its proper divisors (25124772798).

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

21156817986 is a wasteful number, since it uses less digits than its factorization.

21156817986 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16335 (or 16332 counting only the distinct ones).

The product of its digits is 1451520, while the sum is 54.

The spelling of 21156817986 in words is "twenty-one billion, one hundred fifty-six million, eight hundred seventeen thousand, nine hundred eighty-six".