21638646 has 12 divisors (see below), whose sum is σ = 46883772. Its totient is φ = 7212876.

The previous prime is 21638633. The next prime is 21638647. The reversal of 21638646 is 64683612.

21638646 is a `hidden beast` number, since 2 + 1 + 6 + 3 + 8 + 646 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 21638646.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21638647) 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, 601056 + ... + 601091.

It is an arithmetic number, because the mean of its divisors is an integer number (3906981).

Almost surely, 2^21638646 is an apocalyptic number.

21638646 is an abundant number, since it is smaller than the sum of its proper divisors (25245126).

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

21638646 is a wasteful number, since it uses less digits than its factorization.

21638646 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1202155 (or 1202152 counting only the distinct ones).

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

The square root of 21638646 is about 4651.7358050517. The cubic root of 21638646 is about 278.6613225804.

The spelling of 21638646 in words is "twenty-one million, six hundred thirty-eight thousand, six hundred forty-six".