665256661 has 4 divisors (see below), whose sum is σ = 665337024. Its totient is φ = 665176300.

The previous prime is 665256593. The next prime is 665256721. The reversal of 665256661 is 166652566.

665256661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 665256661 - 2⁷ = 665256533 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665256061) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26125 + ... + 44866.

It is an arithmetic number, because the mean of its divisors is an integer number (166334256).

Almost surely, 2^665256661 is an apocalyptic number.

It is an amenable number.

665256661 is a deficient number, since it is larger than the sum of its proper divisors (80363).

665256661 is an equidigital number, since it uses as much as digits as its factorization.

665256661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80362.

The product of its digits is 388800, while the sum is 43.

The square root of 665256661 is about 25792.5698797154. The cubic root of 665256661 is about 872.9641533278.

The spelling of 665256661 in words is "six hundred sixty-five million, two hundred fifty-six thousand, six hundred sixty-one".