261778581 has 16 divisors (see below), whose sum is σ = 393611200. Its totient is φ = 171913104.

The previous prime is 261778549. The next prime is 261778591. The reversal of 261778581 is 185877162.

It is a happy number.

261778581 is a `hidden beast` number, since 2 + 61 + 7 + 7 + 8 + 581 = 666.

It is not a de Polignac number, because 261778581 - 2⁵ = 261778549 is a prime.

It is a super-2 number, since 2×261778581² = 137056050940747122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261778591) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 70546 + ... + 74163.

It is an arithmetic number, because the mean of its divisors is an integer number (24600700).

Almost surely, 2^261778581 is an apocalyptic number.

It is an amenable number.

261778581 is a deficient number, since it is larger than the sum of its proper divisors (131832619).

261778581 is a wasteful number, since it uses less digits than its factorization.

261778581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144785 (or 144779 counting only the distinct ones).

The product of its digits is 188160, while the sum is 45.

The square root of 261778581 is about 16179.5729548094. The cubic root of 261778581 is about 639.7024829711.

The spelling of 261778581 in words is "two hundred sixty-one million, seven hundred seventy-eight thousand, five hundred eighty-one".