21664836 has 18 divisors (see below), whose sum is σ = 54763982. Its totient is φ = 7221600.

The previous prime is 21664831. The next prime is 21664837. The reversal of 21664836 is 63846612.

21664836 is a `hidden beast` number, since 2 + 1 + 6 + 648 + 3 + 6 = 666.

It can be written as a sum of positive squares in only one way, i.e., 18922500 + 2742336 = 4350^2 + 1656^2 .

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: 601801 = 21664836 / (2 + 1 + 6 + 6 + 4 + 8 + 3 + 6).

It is a self number, because there is not a number n which added to its sum of digits gives 21664836.

It is not an unprimeable number, because it can be changed into a prime (21664831) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 300865 + ... + 300936.

Almost surely, 2^21664836 is an apocalyptic number.

It is an amenable number.

21664836 is an abundant number, since it is smaller than the sum of its proper divisors (33099146).

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

21664836 is a wasteful number, since it uses less digits than its factorization.

21664836 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 601811 (or 601806 counting only the distinct ones).

The product of its digits is 41472, while the sum is 36.

The square root of 21664836 is about 4654.5500319580. The cubic root of 21664836 is about 278.7737017256.

It can be divided in two parts, 21664 and 836, that added together give a square (22500 = 150²).

The spelling of 21664836 in words is "twenty-one million, six hundred sixty-four thousand, eight hundred thirty-six".