21861515520 has 864 divisors, whose sum is σ = 88874755200. Its totient is φ = 5072191488.

The previous prime is 21861515509. The next prime is 21861515587. The reversal of 21861515520 is 2551516812.

21861515520 is a `hidden beast` number, since 2 + 1 + 8 + 615 + 15 + 5 + 20 = 666.

It is a tau number, because it is divible by the number of its divisors (864).

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

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, 110972062 + ... + 110972258.

It is an arithmetic number, because the mean of its divisors is an integer number (102864300).

Almost surely, 2^21861515520 is an apocalyptic number.

21861515520 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 21861515520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44437377600).

21861515520 is an abundant number, since it is smaller than the sum of its proper divisors (67013239680).

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

21861515520 is a wasteful number, since it uses less digits than its factorization.

21861515520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 272 (or 239 counting only the distinct ones).

The product of its (nonzero) digits is 24000, while the sum is 36.

The spelling of 21861515520 in words is "twenty-one billion, eight hundred sixty-one million, five hundred fifteen thousand, five hundred twenty".