21805980 has 72 divisors (see below), whose sum is σ = 71034768. Its totient is φ = 4983552.

The previous prime is 21805967. The next prime is 21805981. The reversal of 21805980 is 8950812.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21805981) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 769 + ... + 6648.

It is an arithmetic number, because the mean of its divisors is an integer number (986594).

Almost surely, 2^21805980 is an apocalyptic number.

21805980 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 21805980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35517384).

21805980 is an abundant number, since it is smaller than the sum of its proper divisors (49228788).

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

21805980 is a wasteful number, since it uses less digits than its factorization.

21805980 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7443 (or 7434 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 33.

The square root of 21805980 is about 4669.6873557017. The cubic root of 21805980 is about 279.3777850069.

The spelling of 21805980 in words is "twenty-one million, eight hundred five thousand, nine hundred eighty".