216821287656 has 24 divisors (see below), whose sum is σ = 587224320930. Its totient is φ = 72273762528.

The previous prime is 216821287603. The next prime is 216821287667. The reversal of 216821287656 is 656782128612.

It can be written as a sum of positive squares in only one way, i.e., 150908940900 + 65912346756 = 388470^2 + 256734^2 .

It is a tau number, because it is divible by the number of its divisors (24).

It is a super-2 number, since 2×216821287656² (a number of 23 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1505703315 + ... + 1505703458.

Almost surely, 2^216821287656 is an apocalyptic number.

It is an amenable number.

216821287656 is an abundant number, since it is smaller than the sum of its proper divisors (370403033274).

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

216821287656 is a wasteful number, since it uses less digits than its factorization.

216821287656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3011406785 (or 3011406778 counting only the distinct ones).

The product of its digits is 3870720, while the sum is 54.

The spelling of 216821287656 in words is "two hundred sixteen billion, eight hundred twenty-one million, two hundred eighty-seven thousand, six hundred fifty-six".