665563661561 has 2 divisors, whose sum is σ = 665563661562. Its totient is φ = 665563661560.

The previous prime is 665563661513. The next prime is 665563661597. The reversal of 665563661561 is 165166365566.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 624661026025 + 40902635536 = 790355^2 + 202244^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-665563661561 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 665563661497 and 665563661506.

It is not a weakly prime, because it can be changed into another prime (665563661501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332781830780 + 332781830781.

It is an arithmetic number, because the mean of its divisors is an integer number (332781830781).

Almost surely, 2^665563661561 is an apocalyptic number.

It is an amenable number.

665563661561 is a deficient number, since it is larger than the sum of its proper divisors (1).

665563661561 is an equidigital number, since it uses as much as digits as its factorization.

665563661561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 17496000, while the sum is 56.

The spelling of 665563661561 in words is "six hundred sixty-five billion, five hundred sixty-three million, six hundred sixty-one thousand, five hundred sixty-one".