261831 has 4 divisors (see below), whose sum is σ = 349112. Its totient is φ = 174552.

The previous prime is 261823. The next prime is 261847. The reversal of 261831 is 138162.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 261831 - 2³ = 261823 is a prime.

It is a super-2 number, since 2×261831² = 137110945122, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

261831 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 261798 and 261807.

It is a congruent number.

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 3 ways as a sum of consecutive naturals, for example, 43636 + ... + 43641.

It is an arithmetic number, because the mean of its divisors is an integer number (87278).

261831 is a Friedman number, since it can be written as 8^6-311-2, using all its digits and the basic arithmetic operations.

2²⁶¹⁸³¹ is an apocalyptic number.

261831 is a deficient number, since it is larger than the sum of its proper divisors (87281).

261831 is an equidigital number, since it uses as much as digits as its factorization.

261831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87280.

The product of its digits is 288, while the sum is 21.

The square root of 261831 is about 511.6942446422. The cubic root of 261831 is about 63.9745178502.

Adding to 261831 its reverse (138162), we get a palindrome (399993).

The spelling of 261831 in words is "two hundred sixty-one thousand, eight hundred thirty-one".