21665112020 has 24 divisors (see below), whose sum is σ = 45522241800. Its totient is φ = 8661186432.

The previous prime is 21665112017. The next prime is 21665112037. The reversal of 21665112020 is 2021156612.

It can be written as a sum of positive squares in 4 ways, for example, as 14729220496 + 6935891524 = 121364^2 + 83282^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 266975 + ... + 338534.

It is an arithmetic number, because the mean of its divisors is an integer number (1896760075).

Almost surely, 2^21665112020 is an apocalyptic number.

21665112020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21665112020 is an abundant number, since it is smaller than the sum of its proper divisors (23857129780).

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

21665112020 is a wasteful number, since it uses less digits than its factorization.

21665112020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 607307 (or 607305 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 26.

Adding to 21665112020 its reverse (2021156612), we get a palindrome (23686268632).

The spelling of 21665112020 in words is "twenty-one billion, six hundred sixty-five million, one hundred twelve thousand, twenty".