21191661857520 has 2880 divisors, whose sum is σ = 100794805862400. Its totient is φ = 3863982735360.

The previous prime is 21191661857519. The next prime is 21191661857579. The reversal of 21191661857520 is 2575816619112.

21191661857520 is a `hidden beast` number, since 2 + 1 + 1 + 9 + 1 + 6 + 61 + 8 + 57 + 520 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 575 ways as a sum of consecutive naturals, for example, 20396209161 + ... + 20396210199.

It is an arithmetic number, because the mean of its divisors is an integer number (34998196480).

Almost surely, 2^{21191661857520} is an apocalyptic number.

21191661857520 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 21191661857520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (50397402931200).

21191661857520 is an abundant number, since it is smaller than the sum of its proper divisors (79603144004880).

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

21191661857520 is a wasteful number, since it uses less digits than its factorization.

21191661857520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1196 (or 1170 counting only the distinct ones).

The product of its (nonzero) digits is 1814400, while the sum is 54.

The spelling of 21191661857520 in words is "twenty-one trillion, one hundred ninety-one billion, six hundred sixty-one million, eight hundred fifty-seven thousand, five hundred twenty".