21666403920 has 80 divisors (see below), whose sum is σ = 76760979840. Its totient is φ = 4952320512.

The previous prime is 21666403919. The next prime is 21666403939. The reversal of 21666403920 is 2930466612.

It is a tau number, because it is divible by the number of its divisors (80).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6446655 + ... + 6450014.

It is an arithmetic number, because the mean of its divisors is an integer number (959512248).

Almost surely, 2^21666403920 is an apocalyptic number.

21666403920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21666403920 is an abundant number, since it is smaller than the sum of its proper divisors (55094575920).

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

21666403920 is a wasteful number, since it uses less digits than its factorization.

21666403920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12896692 (or 12896686 counting only the distinct ones).

The product of its (nonzero) digits is 93312, while the sum is 39.

The spelling of 21666403920 in words is "twenty-one billion, six hundred sixty-six million, four hundred three thousand, nine hundred twenty".