21639864 has 32 divisors (see below), whose sum is σ = 54245520. Its totient is φ = 7193856.

The previous prime is 21639833. The next prime is 21639869. The reversal of 21639864 is 46893612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21639869) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9982 + ... + 11954.

Almost surely, 2^21639864 is an apocalyptic number.

21639864 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21639864 is an abundant number, since it is smaller than the sum of its proper divisors (32605656).

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

21639864 is a wasteful number, since it uses less digits than its factorization.

21639864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2439 (or 2435 counting only the distinct ones).

The product of its digits is 62208, while the sum is 39.

The square root of 21639864 is about 4651.8667220805. The cubic root of 21639864 is about 278.6665509285. Note that the first 3 decimals are identical.

The spelling of 21639864 in words is "twenty-one million, six hundred thirty-nine thousand, eight hundred sixty-four".