21666020 has 12 divisors (see below), whose sum is σ = 45498684. Its totient is φ = 8666400.

The previous prime is 21666019. The next prime is 21666037. The reversal of 21666020 is 2066612.

It can be written as a sum of positive squares in 2 ways, for example, as 14092516 + 7573504 = 3754^2 + 2752^2 .

It is a hoax number, since the sum of its digits (23) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 541631 + ... + 541670.

It is an arithmetic number, because the mean of its divisors is an integer number (3791557).

Almost surely, 2^21666020 is an apocalyptic number.

21666020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21666020 is an abundant number, since it is smaller than the sum of its proper divisors (23832664).

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

21666020 is a wasteful number, since it uses less digits than its factorization.

21666020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1083310 (or 1083308 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 21666020 is about 4654.6772175952. The cubic root of 21666020 is about 278.7787800323.

The spelling of 21666020 in words is "twenty-one million, six hundred sixty-six thousand, twenty".