21517980 has 48 divisors (see below), whose sum is σ = 65729664. Its totient is φ = 5216320.

The previous prime is 21517973. The next prime is 21518009. The reversal of 21517980 is 8971512.

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

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 15 ways as a sum of consecutive naturals, for example, 15642 + ... + 16961.

It is an arithmetic number, because the mean of its divisors is an integer number (1369368).

Almost surely, 2^21517980 is an apocalyptic number.

21517980 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21517980 is an abundant number, since it is smaller than the sum of its proper divisors (44211684).

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

21517980 is a wasteful number, since it uses less digits than its factorization.

21517980 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32626 (or 32624 counting only the distinct ones).

The product of its (nonzero) digits is 5040, while the sum is 33.

The square root of 21517980 is about 4638.7476758280. The cubic root of 21517980 is about 278.1423800106.

The spelling of 21517980 in words is "twenty-one million, five hundred seventeen thousand, nine hundred eighty".