661666565477 has 2 divisors, whose sum is σ = 661666565478. Its totient is φ = 661666565476.

The previous prime is 661666565459. The next prime is 661666565557. The reversal of 661666565477 is 774565666166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 456434008801 + 205232556676 = 675599^2 + 453026^2 .

It is a cyclic number.

It is not a de Polignac number, because 661666565477 - 2¹⁶ = 661666499941 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661666565447) 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, 330833282738 + 330833282739.

It is an arithmetic number, because the mean of its divisors is an integer number (330833282739).

Almost surely, 2^661666565477 is an apocalyptic number.

It is an amenable number.

661666565477 is a deficient number, since it is larger than the sum of its proper divisors (1).

661666565477 is an equidigital number, since it uses as much as digits as its factorization.

661666565477 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 228614400, while the sum is 65.

The spelling of 661666565477 in words is "six hundred sixty-one billion, six hundred sixty-six million, five hundred sixty-five thousand, four hundred seventy-seven".