640670491 has 2 divisors, whose sum is σ = 640670492. Its totient is φ = 640670490.

The previous prime is 640670479. The next prime is 640670507. The reversal of 640670491 is 194076046.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 640670491 - 2⁹ = 640669979 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 640670491.

It is not a weakly prime, because it can be changed into another prime (640670431) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320335245 + 320335246.

It is an arithmetic number, because the mean of its divisors is an integer number (320335246).

Almost surely, 2^640670491 is an apocalyptic number.

640670491 is a deficient number, since it is larger than the sum of its proper divisors (1).

640670491 is an equidigital number, since it uses as much as digits as its factorization.

640670491 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 36288, while the sum is 37.

The square root of 640670491 is about 25311.4695543345. The cubic root of 640670491 is about 862.0747145364.

The spelling of 640670491 in words is "six hundred forty million, six hundred seventy thousand, four hundred ninety-one".