21879940 has 12 divisors (see below), whose sum is σ = 45947916. Its totient is φ = 8751968.

The previous prime is 21879929. The next prime is 21879943. The reversal of 21879940 is 4997812.

It can be written as a sum of positive squares in 2 ways, for example, as 10536516 + 11343424 = 3246^2 + 3368^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21879893 and 21879902.

It is not an unprimeable number, because it can be changed into a prime (21879943) 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, 546979 + ... + 547018.

It is an arithmetic number, because the mean of its divisors is an integer number (3828993).

Almost surely, 2^21879940 is an apocalyptic number.

21879940 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21879940 is an abundant number, since it is smaller than the sum of its proper divisors (24067976).

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

21879940 is a wasteful number, since it uses less digits than its factorization.

21879940 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1094006 (or 1094004 counting only the distinct ones).

The product of its (nonzero) digits is 36288, while the sum is 40.

The square root of 21879940 is about 4677.5998118693. The cubic root of 21879940 is about 279.6932865963.

The spelling of 21879940 in words is "twenty-one million, eight hundred seventy-nine thousand, nine hundred forty".