261581 has 2 divisors, whose sum is σ = 261582. Its totient is φ = 261580.

The previous prime is 261577. The next prime is 261587. The reversal of 261581 is 185162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 259081 + 2500 = 509^2 + 50^2 .

It is a cyclic number.

It is not a de Polignac number, because 261581 - 2² = 261577 is a prime.

It is a super-2 number, since 2×261581² = 136849239122, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261587) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130790 + 130791.

It is an arithmetic number, because the mean of its divisors is an integer number (130791).

2²⁶¹⁵⁸¹ is an apocalyptic number.

It is an amenable number.

261581 is a deficient number, since it is larger than the sum of its proper divisors (1).

261581 is an equidigital number, since it uses as much as digits as its factorization.

261581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 480, while the sum is 23.

The square root of 261581 is about 511.4498997947. The cubic root of 261581 is about 63.9541501035.

The spelling of 261581 in words is "two hundred sixty-one thousand, five hundred eighty-one".