21639872 has 56 divisors (see below), whose sum is σ = 45732192. Its totient is φ = 10137600.

The previous prime is 21639869. The next prime is 21639889. The reversal of 21639872 is 27893612.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 89672 + ... + 89912.

Almost surely, 2^21639872 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21639872, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22866096).

21639872 is an abundant number, since it is smaller than the sum of its proper divisors (24092320).

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

21639872 is a wasteful number, since it uses less digits than its factorization.

21639872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 337 (or 327 counting only the distinct ones).

The product of its digits is 36288, while the sum is 38.

The square root of 21639872 is about 4651.8675819503. The cubic root of 21639872 is about 278.6665852684. Note that the first 3 decimals are identical.

The spelling of 21639872 in words is "twenty-one million, six hundred thirty-nine thousand, eight hundred seventy-two".