21105505620 has 72 divisors (see below), whose sum is σ = 64299722760. Its totient is φ = 5603546880.

The previous prime is 21105505609. The next prime is 21105505637. The reversal of 21105505620 is 2650550112.

21105505620 is a `hidden beast` number, since 21 + 10 + 5 + 5 + 0 + 5 + 620 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 11910229956 + 9195275664 = 109134^2 + 95892^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 214791 + ... + 297230.

It is an arithmetic number, because the mean of its divisors is an integer number (893051705).

Almost surely, 2^21105505620 is an apocalyptic number.

21105505620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21105505620 is an abundant number, since it is smaller than the sum of its proper divisors (43194217140).

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

21105505620 is a wasteful number, since it uses less digits than its factorization.

21105505620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 512265 (or 512260 counting only the distinct ones).

The product of its (nonzero) digits is 3000, while the sum is 27.

The spelling of 21105505620 in words is "twenty-one billion, one hundred five million, five hundred five thousand, six hundred twenty".