21856644 has 18 divisors (see below), whose sum is σ = 55248830. Its totient is φ = 7285536.

The previous prime is 21856621. The next prime is 21856657. The reversal of 21856644 is 44665812.

21856644 is a `hidden beast` number, since 2 + 1 + 8 + 5 + 6 + 644 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21068100 + 788544 = 4590^2 + 888^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 607129 = 21856644 / (2 + 1 + 8 + 5 + 6 + 6 + 4 + 4).

It is a junction number, because it is equal to n+sod(n) for n = 21856599 and 21856608.

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, 303529 + ... + 303600.

Almost surely, 2^21856644 is an apocalyptic number.

It is an amenable number.

21856644 is an abundant number, since it is smaller than the sum of its proper divisors (33392186).

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

21856644 is a wasteful number, since it uses less digits than its factorization.

21856644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 607139 (or 607134 counting only the distinct ones).

The product of its digits is 46080, while the sum is 36.

The square root of 21856644 is about 4675.1089826869. The cubic root of 21856644 is about 279.5939863750.

It can be divided in two parts, 21856 and 644, that added together give a square (22500 = 150²).

The spelling of 21856644 in words is "twenty-one million, eight hundred fifty-six thousand, six hundred forty-four".