261809 has 4 divisors (see below), whose sum is σ = 273216. Its totient is φ = 250404.

The previous prime is 261799. The next prime is 261823. The reversal of 261809 is 908162.

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 a cyclic number.

It is not a de Polignac number, because 261809 - 2¹² = 257713 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

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 261809.

It is not an unprimeable number, because it can be changed into a prime (261509) 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, 5669 + ... + 5714.

It is an arithmetic number, because the mean of its divisors is an integer number (68304).

2²⁶¹⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

261809 is a deficient number, since it is larger than the sum of its proper divisors (11407).

261809 is a wasteful number, since it uses less digits than its factorization.

261809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11406.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 261809 is about 511.6727469780. The cubic root of 261809 is about 63.9727260089.

The spelling of 261809 in words is "two hundred sixty-one thousand, eight hundred nine".