661560665261 has 2 divisors, whose sum is σ = 661560665262. Its totient is φ = 661560665260.

The previous prime is 661560665179. The next prime is 661560665273. The reversal of 661560665261 is 162566065166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 440091599236 + 221469066025 = 663394^2 + 470605^2 .

It is a cyclic number.

It is not a de Polignac number, because 661560665261 - 2³⁴ = 644380796077 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661560661261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330780332630 + 330780332631.

It is an arithmetic number, because the mean of its divisors is an integer number (330780332631).

Almost surely, 2^661560665261 is an apocalyptic number.

It is an amenable number.

661560665261 is a deficient number, since it is larger than the sum of its proper divisors (1).

661560665261 is an equidigital number, since it uses as much as digits as its factorization.

661560665261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2332800, while the sum is 50.

The spelling of 661560665261 in words is "six hundred sixty-one billion, five hundred sixty million, six hundred sixty-five thousand, two hundred sixty-one".