1666128209 has 2 divisors, whose sum is σ = 1666128210. Its totient is φ = 1666128208.

The previous prime is 1666128179. The next prime is 1666128223. The reversal of 1666128209 is 9028216661.

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., 1245878209 + 420250000 = 35297^2 + 20500^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1666128209 is a prime.

It is not a weakly prime, because it can be changed into another prime (1666122209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833064104 + 833064105.

It is an arithmetic number, because the mean of its divisors is an integer number (833064105).

Almost surely, 2^1666128209 is an apocalyptic number.

It is an amenable number.

1666128209 is a deficient number, since it is larger than the sum of its proper divisors (1).

1666128209 is an equidigital number, since it uses as much as digits as its factorization.

1666128209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 62208, while the sum is 41.

The square root of 1666128209 is about 40818.2337809955. The cubic root of 1666128209 is about 1185.5034053126.

The spelling of 1666128209 in words is "one billion, six hundred sixty-six million, one hundred twenty-eight thousand, two hundred nine".