261808 has 10 divisors (see below), whose sum is σ = 507284. Its totient is φ = 130896.

The previous prime is 261799. The next prime is 261823. The reversal of 261808 is 808162.

It is a nialpdrome in base 13.

It is an unprimeable number.

261808 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8166 + ... + 8197.

2²⁶¹⁸⁰⁸ is an apocalyptic number.

261808 is the 274-th centered heptagonal number.

It is an amenable number.

261808 is a deficient number, since it is larger than the sum of its proper divisors (245476).

261808 is a wasteful number, since it uses less digits than its factorization.

261808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16371 (or 16365 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 25.

The square root of 261808 is about 511.6717697900. The cubic root of 261808 is about 63.9726445592.

The spelling of 261808 in words is "two hundred sixty-one thousand, eight hundred eight".