261689 has 4 divisors (see below), whose sum is σ = 263424. Its totient is φ = 259956.

The previous prime is 261673. The next prime is 261697. The reversal of 261689 is 986162.

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 261689 - 2⁴ = 261673 is a prime.

It is a super-2 number, since 2×261689² = 136962265442, which contains 22 as substring.

It is an Ulam 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 (261619) 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, 617 + ... + 950.

It is an arithmetic number, because the mean of its divisors is an integer number (65856).

2²⁶¹⁶⁸⁹ is an apocalyptic number.

It is an amenable number.

261689 is a deficient number, since it is larger than the sum of its proper divisors (1735).

261689 is a wasteful number, since it uses less digits than its factorization.

261689 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1734.

The product of its digits is 5184, while the sum is 32.

The square root of 261689 is about 511.5554710879. Note that the first 3 decimals coincide. The cubic root of 261689 is about 63.9629505615.

The spelling of 261689 in words is "two hundred sixty-one thousand, six hundred eighty-nine".