661515661 has 2 divisors, whose sum is σ = 661515662. Its totient is φ = 661515660.

The previous prime is 661515649. The next prime is 661515671. The reversal of 661515661 is 166515166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 660181636 + 1334025 = 25694^2 + 1155^2 .

It is a cyclic number.

It is not a de Polignac number, because 661515661 - 2⁵ = 661515629 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 661515661.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661515671) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330757830 + 330757831.

It is an arithmetic number, because the mean of its divisors is an integer number (330757831).

Almost surely, 2^661515661 is an apocalyptic number.

It is an amenable number.

661515661 is a deficient number, since it is larger than the sum of its proper divisors (1).

661515661 is an equidigital number, since it uses as much as digits as its factorization.

661515661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 32400, while the sum is 37.

The square root of 661515661 is about 25719.9467534441. The cubic root of 661515661 is about 871.3247361249.

The spelling of 661515661 in words is "six hundred sixty-one million, five hundred fifteen thousand, six hundred sixty-one".