21881904 has 40 divisors (see below), whose sum is σ = 61668672. Its totient is φ = 6630720.

The previous prime is 21881903. The next prime is 21881917. The reversal of 21881904 is 40918812.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21881903) 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, 20194 + ... + 21249.

Almost surely, 2^21881904 is an apocalyptic number.

21881904 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21881904 is an abundant number, since it is smaller than the sum of its proper divisors (39786768).

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

21881904 is a wasteful number, since it uses less digits than its factorization.

21881904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41465 (or 41459 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 33.

The square root of 21881904 is about 4677.8097438866. The cubic root of 21881904 is about 279.7016550101.

The spelling of 21881904 in words is "twenty-one million, eight hundred eighty-one thousand, nine hundred four".