261566721 has 24 divisors (see below), whose sum is σ = 416351936. Its totient is φ = 157217760.

The previous prime is 261566707. The next prime is 261566729. The reversal of 261566721 is 127665162.

It is a happy number.

261566721 is a `hidden beast` number, since 26 + 1 + 566 + 72 + 1 = 666.

It is not a de Polignac number, because 261566721 - 2¹³ = 261558529 is a prime.

It is not an unprimeable number, because it can be changed into a prime (261566729) 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 23 ways as a sum of consecutive naturals, for example, 20965 + ... + 31026.

Almost surely, 2^261566721 is an apocalyptic number.

It is an amenable number.

261566721 is a deficient number, since it is larger than the sum of its proper divisors (154785215).

261566721 is a wasteful number, since it uses less digits than its factorization.

261566721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52053 (or 52050 counting only the distinct ones).

The product of its digits is 30240, while the sum is 36.

The square root of 261566721 is about 16173.0244852347. The cubic root of 261566721 is about 639.5298638755.

The spelling of 261566721 in words is "two hundred sixty-one million, five hundred sixty-six thousand, seven hundred twenty-one".