261705 has 16 divisors (see below), whose sum is σ = 426240. Its totient is φ = 137088.

The previous prime is 261697. The next prime is 261707. The reversal of 261705 is 507162.

It is not a de Polignac number, because 261705 - 2³ = 261697 is a prime.

261705 is a lucky number.

It is a nialpdrome in base 8.

It is a zygodrome in base 8.

It is not an unprimeable number, because it can be changed into a prime (261707) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 976 + ... + 1214.

It is an arithmetic number, because the mean of its divisors is an integer number (26640).

2²⁶¹⁷⁰⁵ is an apocalyptic number.

It is an amenable number.

261705 is a deficient number, since it is larger than the sum of its proper divisors (164535).

261705 is a wasteful number, since it uses less digits than its factorization.

261705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 320.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 261705 is about 511.5711094266. The cubic root of 261705 is about 63.9642541271.

Adding to 261705 its sum of digits (21), we get a triangular number (261726 = T₇₂₃).

Adding to 261705 its reverse (507162), we get a palindrome (768867).

The spelling of 261705 in words is "two hundred sixty-one thousand, seven hundred five".