640375691 has 2 divisors, whose sum is σ = 640375692. Its totient is φ = 640375690.

The previous prime is 640375663. The next prime is 640375693. The reversal of 640375691 is 196573046.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640375691 is a prime.

It is a Sophie Germain prime.

Together with 640375693, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (640375693) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320187845 + 320187846.

It is an arithmetic number, because the mean of its divisors is an integer number (320187846).

Almost surely, 2^640375691 is an apocalyptic number.

640375691 is a deficient number, since it is larger than the sum of its proper divisors (1).

640375691 is an equidigital number, since it uses as much as digits as its factorization.

640375691 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 136080, while the sum is 41.

The square root of 640375691 is about 25305.6454373328. The cubic root of 640375691 is about 861.9424683872.

The spelling of 640375691 in words is "six hundred forty million, three hundred seventy-five thousand, six hundred ninety-one".