21664980 has 72 divisors (see below), whose sum is σ = 67513992. Its totient is φ = 5619456.

The previous prime is 21664967. The next prime is 21665009. The reversal of 21664980 is 8946612.

21664980 is a `hidden beast` number, since 2 + 1 + 6 + 649 + 8 + 0 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 13439556 + 8225424 = 3666^2 + 2868^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

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 23 ways as a sum of consecutive naturals, for example, 5034 + ... + 8286.

Almost surely, 2^21664980 is an apocalyptic number.

21664980 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21664980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33756996).

21664980 is an abundant number, since it is smaller than the sum of its proper divisors (45849012).

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

21664980 is a wasteful number, since it uses less digits than its factorization.

21664980 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3305 (or 3300 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 21664980 is about 4654.5655006671. The cubic root of 21664980 is about 278.7743193673.

The spelling of 21664980 in words is "twenty-one million, six hundred sixty-four thousand, nine hundred eighty".