261681 has 16 divisors (see below), whose sum is σ = 422784. Its totient is φ = 140544.

The previous prime is 261673. The next prime is 261697. The reversal of 261681 is 186162.

It is not a de Polignac number, because 261681 - 2³ = 261673 is a prime.

It is a super-2 number, since 2×261681² = 136953891522, which contains 22 as substring.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 261681.

It is not an unprimeable number, because it can be changed into a prime (261601) 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, 10 + ... + 723.

It is an arithmetic number, because the mean of its divisors is an integer number (26424).

2²⁶¹⁶⁸¹ is an apocalyptic number.

261681 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

261681 is a deficient number, since it is larger than the sum of its proper divisors (161103).

261681 is a wasteful number, since it uses less digits than its factorization.

261681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 760.

The product of its digits is 576, while the sum is 24.

The square root of 261681 is about 511.5476517393. The cubic root of 261681 is about 63.9622987588.

The spelling of 261681 in words is "two hundred sixty-one thousand, six hundred eighty-one".