21178256856 has 128 divisors (see below), whose sum is σ = 56136499200. Its totient is φ = 6648445440.

The previous prime is 21178256849. The next prime is 21178256867. The reversal of 21178256856 is 65865287112.

It is a super-2 number, since 2×21178256856² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21178256799 and 21178256808.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5005750 + ... + 5009978.

It is an arithmetic number, because the mean of its divisors is an integer number (438566400).

Almost surely, 2^21178256856 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 21178256856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28068249600).

21178256856 is an abundant number, since it is smaller than the sum of its proper divisors (34958242344).

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

21178256856 is a wasteful number, since it uses less digits than its factorization.

21178256856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4449 (or 4445 counting only the distinct ones).

The product of its digits is 1612800, while the sum is 51.

The spelling of 21178256856 in words is "twenty-one billion, one hundred seventy-eight million, two hundred fifty-six thousand, eight hundred fifty-six".