21123265536 has 220 divisors, whose sum is σ = 63406881252. Its totient is φ = 7004454912.

The previous prime is 21123265529. The next prime is 21123265633. The reversal of 21123265536 is 63556232112.

21123265536 is a `hidden beast` number, since 2 + 112 + 3 + 2 + 6 + 5 + 536 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 14147675136 + 6975590400 = 118944^2 + 83520^2 .

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

It is a self number, because there is not a number n which added to its sum of digits gives 21123265536.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 19325406 + ... + 19326498.

Almost surely, 2^21123265536 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21123265536, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31703440626).

21123265536 is an abundant number, since it is smaller than the sum of its proper divisors (42283615716).

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

21123265536 is a wasteful number, since it uses less digits than its factorization.

21123265536 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1358 (or 1331 counting only the distinct ones).

The product of its digits is 64800, while the sum is 36.

Adding to 21123265536 its reverse (63556232112), we get a palindrome (84679497648).

The spelling of 21123265536 in words is "twenty-one billion, one hundred twenty-three million, two hundred sixty-five thousand, five hundred thirty-six".