21660831613 has 4 divisors (see below), whose sum is σ = 21664558588. Its totient is φ = 21657104640.

The previous prime is 21660831581. The next prime is 21660831623. The reversal of 21660831613 is 31613806612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 20654863524 + 1005968089 = 143718^2 + 31717^2 .

It is a cyclic number.

It is not a de Polignac number, because 21660831613 - 2⁵ = 21660831581 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21660831623) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1854756 + ... + 1866397.

It is an arithmetic number, because the mean of its divisors is an integer number (5416139647).

Almost surely, 2^21660831613 is an apocalyptic number.

It is an amenable number.

21660831613 is a deficient number, since it is larger than the sum of its proper divisors (3726975).

21660831613 is an equidigital number, since it uses as much as digits as its factorization.

21660831613 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3726974.

The product of its (nonzero) digits is 31104, while the sum is 37.

The spelling of 21660831613 in words is "twenty-one billion, six hundred sixty million, eight hundred thirty-one thousand, six hundred thirteen".