664239991 has 2 divisors, whose sum is σ = 664239992. Its totient is φ = 664239990.

The previous prime is 664239971. The next prime is 664240009. The reversal of 664239991 is 199932466.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 664239991 - 2⁹ = 664239479 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (664239941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332119995 + 332119996.

It is an arithmetic number, because the mean of its divisors is an integer number (332119996).

Almost surely, 2^664239991 is an apocalyptic number.

664239991 is a deficient number, since it is larger than the sum of its proper divisors (1).

664239991 is an equidigital number, since it uses as much as digits as its factorization.

664239991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 629856, while the sum is 49.

The square root of 664239991 is about 25772.8537612737. The cubic root of 664239991 is about 872.5192278256.

The spelling of 664239991 in words is "six hundred sixty-four million, two hundred thirty-nine thousand, nine hundred ninety-one".