666819191 has 2 divisors, whose sum is σ = 666819192. Its totient is φ = 666819190.

The previous prime is 666819161. The next prime is 666819233. The reversal of 666819191 is 191918666.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 666819191 - 2²² = 662624887 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666819161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333409595 + 333409596.

It is an arithmetic number, because the mean of its divisors is an integer number (333409596).

Almost surely, 2^666819191 is an apocalyptic number.

666819191 is a deficient number, since it is larger than the sum of its proper divisors (1).

666819191 is an equidigital number, since it uses as much as digits as its factorization.

666819191 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 139968, while the sum is 47.

The square root of 666819191 is about 25822.8424268127. The cubic root of 666819191 is about 873.6470807953.

The spelling of 666819191 in words is "six hundred sixty-six million, eight hundred nineteen thousand, one hundred ninety-one".