665615561 has 16 divisors (see below), whose sum is σ = 755279616. Its totient is φ = 581967936.

The previous prime is 665615549. The next prime is 665615593. The reversal of 665615561 is 165516566.

It is a cyclic number.

It is not a de Polignac number, because 665615561 - 2¹⁴ = 665599177 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (665615861) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19991 + ... + 41603.

It is an arithmetic number, because the mean of its divisors is an integer number (47204976).

Almost surely, 2^665615561 is an apocalyptic number.

It is an amenable number.

665615561 is a deficient number, since it is larger than the sum of its proper divisors (89664055).

665615561 is a wasteful number, since it uses less digits than its factorization.

665615561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21752.

The product of its digits is 162000, while the sum is 41.

The square root of 665615561 is about 25799.5263716216. The cubic root of 665615561 is about 873.1211105484.

The spelling of 665615561 in words is "six hundred sixty-five million, six hundred fifteen thousand, five hundred sixty-one".