21659940 has 48 divisors (see below), whose sum is σ = 67388160. Its totient is φ = 5775840.

The previous prime is 21659873. The next prime is 21659947. The reversal of 21659940 is 4995612.

21659940 is a `hidden beast` number, since 21 + 6 + 599 + 40 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21659895 and 21659904.

It is not an unprimeable number, because it can be changed into a prime (21659947) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19516 + ... + 20595.

It is an arithmetic number, because the mean of its divisors is an integer number (1403920).

Almost surely, 2^21659940 is an apocalyptic number.

21659940 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21659940 is an abundant number, since it is smaller than the sum of its proper divisors (45728220).

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

21659940 is a wasteful number, since it uses less digits than its factorization.

21659940 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40129 (or 40121 counting only the distinct ones).

The product of its (nonzero) digits is 19440, while the sum is 36.

The square root of 21659940 is about 4654.0240652579. The cubic root of 21659940 is about 278.7527002761.

The spelling of 21659940 in words is "twenty-one million, six hundred fifty-nine thousand, nine hundred forty".