21918636 has 18 divisors (see below), whose sum is σ = 55405532. Its totient is φ = 7306200.

The previous prime is 21918607. The next prime is 21918649. The reversal of 21918636 is 63681912.

21918636 is a `hidden beast` number, since 2 + 1 + 9 + 18 + 636 = 666.

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: 608851 = 21918636 / (2 + 1 + 9 + 1 + 8 + 6 + 3 + 6).

It is a self number, because there is not a number n which added to its sum of digits gives 21918636.

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, 304390 + ... + 304461.

Almost surely, 2^21918636 is an apocalyptic number.

It is an amenable number.

21918636 is an abundant number, since it is smaller than the sum of its proper divisors (33486896).

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

21918636 is a wasteful number, since it uses less digits than its factorization.

21918636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 608861 (or 608856 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 21918636 is about 4681.7342940410. The cubic root of 21918636 is about 279.8580743317.

The spelling of 21918636 in words is "twenty-one million, nine hundred eighteen thousand, six hundred thirty-six".