21639040 has 32 divisors (see below), whose sum is σ = 51732360. Its totient is φ = 8655360.

The previous prime is 21639001. The next prime is 21639049. The reversal of 21639040 is 4093612.

It is a tau number, because it is divible by the number of its divisors (32).

It is a junction number, because it is equal to n+sod(n) for n = 21638996 and 21639014.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21639049) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16266 + ... + 17545.

Almost surely, 2^21639040 is an apocalyptic number.

21639040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21639040 is an abundant number, since it is smaller than the sum of its proper divisors (30093320).

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

21639040 is an equidigital number, since it uses as much as digits as its factorization.

21639040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33830 (or 33818 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 25.

The square root of 21639040 is about 4651.7781546415. The cubic root of 21639040 is about 278.6630138738.

It can be divided in two parts, 2 and 1639040, that multiplied together give a triangular number (3278080 = T₂₅₆₀).

The spelling of 21639040 in words is "twenty-one million, six hundred thirty-nine thousand, forty".