261857 has 4 divisors (see below), whose sum is σ = 270336. Its totient is φ = 253380.

The previous prime is 261847. The next prime is 261881. The reversal of 261857 is 758162.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 758162 = 2 ⋅379081.

It is a cyclic number.

It is not a de Polignac number, because 261857 - 2⁸ = 261601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261847) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4193 + ... + 4254.

It is an arithmetic number, because the mean of its divisors is an integer number (67584).

2²⁶¹⁸⁵⁷ is an apocalyptic number.

It is an amenable number.

261857 is a deficient number, since it is larger than the sum of its proper divisors (8479).

261857 is an equidigital number, since it uses as much as digits as its factorization.

261857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8478.

The product of its digits is 3360, while the sum is 29.

The square root of 261857 is about 511.7196498084. The cubic root of 261857 is about 63.9766353515.

The spelling of 261857 in words is "two hundred sixty-one thousand, eight hundred fifty-seven".