21856705656 has 64 divisors (see below), whose sum is σ = 58005136800. Its totient is φ = 6839328768.

The previous prime is 21856705609. The next prime is 21856705657. The reversal of 21856705656 is 65650765812.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (51).

It is an alternating number because its digits alternate between even and odd.

It is a junction number, because it is equal to n+sod(n) for n = 21856705599 and 21856705608.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21856705657) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 89856 + ... + 227568.

Almost surely, 2^21856705656 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21856705656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29002568400).

21856705656 is an abundant number, since it is smaller than the sum of its proper divisors (36148431144).

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

21856705656 is a wasteful number, since it uses less digits than its factorization.

21856705656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 138128 (or 138124 counting only the distinct ones).

The product of its (nonzero) digits is 3024000, while the sum is 51.

The spelling of 21856705656 in words is "twenty-one billion, eight hundred fifty-six million, seven hundred five thousand, six hundred fifty-six".