21387636 has 36 divisors (see below), whose sum is σ = 54381600. Its totient is φ = 7087248.

The previous prime is 21387629. The next prime is 21387643. The reversal of 21387636 is 63678312.

It is a happy number.

21387636 is a `hidden beast` number, since 2 + 13 + 8 + 7 + 636 = 666.

It is an interprime number because it is at equal distance from previous prime (21387629) and next prime (21387643).

It is a tau number, because it is divible by the number of its divisors (36).

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 21387636.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4785 + ... + 8103.

It is an arithmetic number, because the mean of its divisors is an integer number (1510600).

Almost surely, 2^21387636 is an apocalyptic number.

It is an amenable number.

21387636 is an abundant number, since it is smaller than the sum of its proper divisors (32993964).

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

21387636 is a wasteful number, since it uses less digits than its factorization.

21387636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3508 (or 3503 counting only the distinct ones).

The product of its digits is 36288, while the sum is 36.

The square root of 21387636 is about 4624.6768535758. The cubic root of 21387636 is about 277.5796313956.

The spelling of 21387636 in words is "twenty-one million, three hundred eighty-seven thousand, six hundred thirty-six".