1666685021 has 2 divisors, whose sum is σ = 1666685022. Its totient is φ = 1666685020.

The previous prime is 1666684993. The next prime is 1666685029. The reversal of 1666685021 is 1205866661.

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., 1217032996 + 449652025 = 34886^2 + 21205^2 .

It is a cyclic number.

It is not a de Polignac number, because 1666685021 - 2¹⁴ = 1666668637 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 1666685021.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1666685029) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833342510 + 833342511.

It is an arithmetic number, because the mean of its divisors is an integer number (833342511).

Almost surely, 2^1666685021 is an apocalyptic number.

It is an amenable number.

1666685021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1666685021 is an equidigital number, since it uses as much as digits as its factorization.

1666685021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 103680, while the sum is 41.

The square root of 1666685021 is about 40825.0538395236. The cubic root of 1666685021 is about 1185.6354537744.

The spelling of 1666685021 in words is "one billion, six hundred sixty-six million, six hundred eighty-five thousand, twenty-one".