665061561 has 6 divisors (see below), whose sum is σ = 960644490. Its totient is φ = 443374368.

The previous prime is 665061493. The next prime is 665061581. The reversal of 665061561 is 165160566.

It can be written as a sum of positive squares in only one way, i.e., 643383225 + 21678336 = 25365^2 + 4656^2 .

It is not a de Polignac number, because 665061561 - 2¹⁴ = 665045177 is a prime.

It is not an unprimeable number, because it can be changed into a prime (665061581) 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 5 ways as a sum of consecutive naturals, for example, 36947856 + ... + 36947873.

It is an arithmetic number, because the mean of its divisors is an integer number (160107415).

Almost surely, 2^665061561 is an apocalyptic number.

It is an amenable number.

665061561 is a deficient number, since it is larger than the sum of its proper divisors (295582929).

665061561 is a wasteful number, since it uses less digits than its factorization.

665061561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73895735 (or 73895732 counting only the distinct ones).

The product of its (nonzero) digits is 32400, while the sum is 36.

The square root of 665061561 is about 25788.7875054257. The cubic root of 665061561 is about 872.8788068400.

The spelling of 665061561 in words is "six hundred sixty-five million, sixty-one thousand, five hundred sixty-one".