261309 has 4 divisors (see below), whose sum is σ = 348416. Its totient is φ = 174204.

The previous prime is 261301. The next prime is 261323. The reversal of 261309 is 903162.

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.

It is not a de Polignac number, because 261309 - 2³ = 261301 is a prime.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261301) 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, 43549 + ... + 43554.

It is an arithmetic number, because the mean of its divisors is an integer number (87104).

2²⁶¹³⁰⁹ is an apocalyptic number.

It is an amenable number.

261309 is a deficient number, since it is larger than the sum of its proper divisors (87107).

261309 is an equidigital number, since it uses as much as digits as its factorization.

261309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87106.

The product of its (nonzero) digits is 324, while the sum is 21.

The square root of 261309 is about 511.1839199349. The cubic root of 261309 is about 63.9319752491.

The spelling of 261309 in words is "two hundred sixty-one thousand, three hundred nine".