261666 has 12 divisors (see below), whose sum is σ = 566982. Its totient is φ = 87216.

The previous prime is 261643. The next prime is 261673. The reversal of 261666 is 666162.

It can be written as a sum of positive squares in only one way, i.e., 245025 + 16641 = 495^2 + 129^2 .

It is a nude number because it is divisible by every one of its digits.

It is a Curzon number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 261666.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 7251 + ... + 7286.

2²⁶¹⁶⁶⁶ is an apocalyptic number.

261666 is an abundant number, since it is smaller than the sum of its proper divisors (305316).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

261666 is a wasteful number, since it uses less digits than its factorization.

261666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14545 (or 14542 counting only the distinct ones).

The product of its digits is 2592, while the sum is 27.

The square root of 261666 is about 511.5329901385. The cubic root of 261666 is about 63.9610765928.

Subtracting 261666 from its reverse (666162), we obtain a square (404496 = 636²).

The spelling of 261666 in words is "two hundred sixty-one thousand, six hundred sixty-six".