21801636021816 has 384 divisors, whose sum is σ = 74610276768000. Its totient is φ = 5864982246144.

The previous prime is 21801636021761. The next prime is 21801636021827. The reversal of 21801636021816 is 61812063610812.

21801636021816 is a `hidden beast` number, since 2 + 1 + 8 + 0 + 1 + 636 + 0 + 2 + 1 + 8 + 1 + 6 = 666.

It is a super-2 number, since 2×21801636021816² (a number of 27 digits) contains 22 as substring.

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, 32446090 + ... + 33111206.

It is an arithmetic number, because the mean of its divisors is an integer number (194297595750).

Almost surely, 2^{21801636021816} 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 21801636021816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37305138384000).

21801636021816 is an abundant number, since it is smaller than the sum of its proper divisors (52808640746184).

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

21801636021816 is a wasteful number, since it uses less digits than its factorization.

21801636021816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 665328 (or 665311 counting only the distinct ones).

The product of its (nonzero) digits is 165888, while the sum is 45.

The spelling of 21801636021816 in words is "twenty-one trillion, eight hundred one billion, six hundred thirty-six million, twenty-one thousand, eight hundred sixteen".