21878540 has 12 divisors (see below), whose sum is σ = 45944976. Its totient is φ = 8751408.

The previous prime is 21878531. The next prime is 21878567. The reversal of 21878540 is 4587812.

It is a self number, because there is not a number n which added to its sum of digits gives 21878540.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 546944 + ... + 546983.

It is an arithmetic number, because the mean of its divisors is an integer number (3828748).

Almost surely, 2^21878540 is an apocalyptic number.

21878540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21878540 is an abundant number, since it is smaller than the sum of its proper divisors (24066436).

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

21878540 is a wasteful number, since it uses less digits than its factorization.

21878540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1093936 (or 1093934 counting only the distinct ones).

The product of its (nonzero) digits is 17920, while the sum is 35.

The square root of 21878540 is about 4677.4501600765. The cubic root of 21878540 is about 279.6873210261.

The spelling of 21878540 in words is "twenty-one million, eight hundred seventy-eight thousand, five hundred forty".