21791078865 has 20 divisors (see below), whose sum is σ = 39062527284. Its totient is φ = 11621908512.

The previous prime is 21791078863. The next prime is 21791078867. The reversal of 21791078865 is 56887019712.

It is an interprime number because it is at equal distance from previous prime (21791078863) and next prime (21791078867).

It can be written as a sum of positive squares in 2 ways, for example, as 5815130049 + 15975948816 = 76257^2 + 126396^2 .

It is not a de Polignac number, because 21791078865 - 2¹ = 21791078863 is a prime.

It is a super-2 number, since 2×21791078865² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21791078863) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 26902162 + ... + 26902971.

Almost surely, 2^21791078865 is an apocalyptic number.

It is an amenable number.

21791078865 is a deficient number, since it is larger than the sum of its proper divisors (17271448419).

21791078865 is an equidigital number, since it uses as much as digits as its factorization.

21791078865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53805150 (or 53805141 counting only the distinct ones).

The product of its (nonzero) digits is 1693440, while the sum is 54.

The spelling of 21791078865 in words is "twenty-one billion, seven hundred ninety-one million, seventy-eight thousand, eight hundred sixty-five".