21556656 has 120 divisors (see below), whose sum is σ = 68090880. Its totient is φ = 6307200.

The previous prime is 21556649. The next prime is 21556673. The reversal of 21556656 is 65665512.

It is a happy number.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21556656.

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, 48885 + ... + 49323.

It is an arithmetic number, because the mean of its divisors is an integer number (567424).

Almost surely, 2^21556656 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 21556656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34045440).

21556656 is an abundant number, since it is smaller than the sum of its proper divisors (46534224).

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

21556656 is a wasteful number, since it uses less digits than its factorization.

21556656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 495 (or 486 counting only the distinct ones).

The product of its digits is 54000, while the sum is 36.

The square root of 21556656 is about 4642.9146018423. The cubic root of 21556656 is about 278.3089228436.

The spelling of 21556656 in words is "twenty-one million, five hundred fifty-six thousand, six hundred fifty-six".