1666683366721 has 2 divisors, whose sum is σ = 1666683366722. Its totient is φ = 1666683366720.

The previous prime is 1666683366709. The next prime is 1666683366737. The reversal of 1666683366721 is 1276633866661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1161844696321 + 504838670400 = 1077889^2 + 710520^2 .

It is a cyclic number.

It is not a de Polignac number, because 1666683366721 - 2³⁹ = 1116927552833 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1666683366721.

It is not a weakly prime, because it can be changed into another prime (1666683369721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833341683360 + 833341683361.

It is an arithmetic number, because the mean of its divisors is an integer number (833341683361).

Almost surely, 2^{1666683366721} is an apocalyptic number.

It is an amenable number.

1666683366721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1666683366721 is an equidigital number, since it uses as much as digits as its factorization.

1666683366721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 47029248, while the sum is 61.

The spelling of 1666683366721 in words is "one trillion, six hundred sixty-six billion, six hundred eighty-three million, three hundred sixty-six thousand, seven hundred twenty-one".