21618809520 has 640 divisors, whose sum is σ = 91811266560. Its totient is φ = 4069232640.

The previous prime is 21618809507. The next prime is 21618809567. The reversal of 21618809520 is 2590881612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is an unprimeable number.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 8074422 + ... + 8077098.

It is an arithmetic number, because the mean of its divisors is an integer number (143455104).

Almost surely, 2^21618809520 is an apocalyptic number.

21618809520 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 21618809520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (45905633280).

21618809520 is an abundant number, since it is smaller than the sum of its proper divisors (70192457040).

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

21618809520 is a wasteful number, since it uses less digits than its factorization.

21618809520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2753 (or 2747 counting only the distinct ones).

The product of its (nonzero) digits is 69120, while the sum is 42.

It can be divided in two parts, 21618 and 809520, that added together give a palindrome (831138).

The spelling of 21618809520 in words is "twenty-one billion, six hundred eighteen million, eight hundred nine thousand, five hundred twenty".