665561257 has 2 divisors, whose sum is σ = 665561258. Its totient is φ = 665561256.

The previous prime is 665561251. The next prime is 665561261. The reversal of 665561257 is 752165566.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 616826896 + 48734361 = 24836^2 + 6981^2 .

It is a cyclic number.

It is not a de Polignac number, because 665561257 - 2¹⁹ = 665036969 is a prime.

It is not a weakly prime, because it can be changed into another prime (665561251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332780628 + 332780629.

It is an arithmetic number, because the mean of its divisors is an integer number (332780629).

Almost surely, 2^665561257 is an apocalyptic number.

It is an amenable number.

665561257 is a deficient number, since it is larger than the sum of its proper divisors (1).

665561257 is an equidigital number, since it uses as much as digits as its factorization.

665561257 is an evil number, because the sum of its binary digits is even.

The product of its digits is 378000, while the sum is 43.

The square root of 665561257 is about 25798.4739277346. The cubic root of 665561257 is about 873.0973654814.

The spelling of 665561257 in words is "six hundred sixty-five million, five hundred sixty-one thousand, two hundred fifty-seven".