640991191 has 2 divisors, whose sum is σ = 640991192. Its totient is φ = 640991190.

The previous prime is 640991179. The next prime is 640991249. The reversal of 640991191 is 191199046.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 640991191 - 2⁵ = 640991159 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 (640991101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320495595 + 320495596.

It is an arithmetic number, because the mean of its divisors is an integer number (320495596).

Almost surely, 2^640991191 is an apocalyptic number.

640991191 is a deficient number, since it is larger than the sum of its proper divisors (1).

640991191 is an equidigital number, since it uses as much as digits as its factorization.

640991191 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 17496, while the sum is 40.

The square root of 640991191 is about 25317.8038344561. The cubic root of 640991191 is about 862.2185332634.

The spelling of 640991191 in words is "six hundred forty million, nine hundred ninety-one thousand, one hundred ninety-one".