261613255681 has 4 divisors (see below), whose sum is σ = 264310299652. Its totient is φ = 258916211712.

The previous prime is 261613255613. The next prime is 261613255691. The reversal of 261613255681 is 186552316162.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 186552316162 = 2 ⋅93276158081.

It can be written as a sum of positive squares in 2 ways, for example, as 35878042225 + 225735213456 = 189415^2 + 475116^2 .

It is not a de Polignac number, because 261613255681 - 2²⁹ = 261076384769 is a prime.

It is a super-2 number, since 2×261613255681² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261613255691) 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, 1348521840 + ... + 1348522033.

It is an arithmetic number, because the mean of its divisors is an integer number (66077574913).

Almost surely, 2^261613255681 is an apocalyptic number.

It is an amenable number.

261613255681 is a deficient number, since it is larger than the sum of its proper divisors (2697043971).

261613255681 is an equidigital number, since it uses as much as digits as its factorization.

261613255681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2697043970.

The product of its digits is 518400, while the sum is 46.

The spelling of 261613255681 in words is "two hundred sixty-one billion, six hundred thirteen million, two hundred fifty-five thousand, six hundred eighty-one".