261891 has 12 divisors (see below), whose sum is σ = 432432. Its totient is φ = 149616.

The previous prime is 261887. The next prime is 261917. The reversal of 261891 is 198162.

It is not a de Polignac number, because 261891 - 2² = 261887 is a prime.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a zygodrome in base 2.

It is not an unprimeable number, because it can be changed into a prime (261881) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2016 + ... + 2141.

It is an arithmetic number, because the mean of its divisors is an integer number (36036).

2²⁶¹⁸⁹¹ is an apocalyptic number.

261891 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

261891 is a deficient number, since it is larger than the sum of its proper divisors (170541).

261891 is a wasteful number, since it uses less digits than its factorization.

261891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4170 (or 4167 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 261891 is about 511.7528700457. The cubic root of 261891 is about 63.9794041801.

The spelling of 261891 in words is "two hundred sixty-one thousand, eight hundred ninety-one".