665331561 has 12 divisors (see below), whose sum is σ = 983384688. Its totient is φ = 433238904.

The previous prime is 665331551. The next prime is 665331593. The reversal of 665331561 is 165133566.

665331561 is a `hidden beast` number, since 6 + 65 + 3 + 31 + 561 = 666.

665331561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 665331561 - 2⁹ = 665331049 is a prime.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (665331551) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 859215 + ... + 859988.

It is an arithmetic number, because the mean of its divisors is an integer number (81948724).

Almost surely, 2^665331561 is an apocalyptic number.

It is an amenable number.

665331561 is a deficient number, since it is larger than the sum of its proper divisors (318053127).

665331561 is a wasteful number, since it uses less digits than its factorization.

665331561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1719252 (or 1719249 counting only the distinct ones).

The product of its digits is 48600, while the sum is 36.

The square root of 665331561 is about 25794.0218073879. The cubic root of 665331561 is about 872.9969138974.

The spelling of 665331561 in words is "six hundred sixty-five million, three hundred thirty-one thousand, five hundred sixty-one".