21517057980 has 288 divisors, whose sum is σ = 75079001088. Its totient is φ = 4937011200.

The previous prime is 21517057979. The next prime is 21517057997. The reversal of 21517057980 is 8975071512.

21517057980 is a `hidden beast` number, since 2 + 1 + 5 + 1 + 70 + 579 + 8 + 0 = 666.

It is a super-2 number, since 2×21517057980² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 4414945 + ... + 4419815.

It is an arithmetic number, because the mean of its divisors is an integer number (260690976).

Almost surely, 2^21517057980 is an apocalyptic number.

21517057980 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 21517057980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37539500544).

21517057980 is an abundant number, since it is smaller than the sum of its proper divisors (53561943108).

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

21517057980 is a wasteful number, since it uses less digits than its factorization.

21517057980 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5017 (or 5012 counting only the distinct ones).

The product of its (nonzero) digits is 176400, while the sum is 45.

The spelling of 21517057980 in words is "twenty-one billion, five hundred seventeen million, fifty-seven thousand, nine hundred eighty".