640808491 has 2 divisors, whose sum is σ = 640808492. Its totient is φ = 640808490.

The previous prime is 640808479. The next prime is 640808501. The reversal of 640808491 is 194808046.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640808491 is a prime.

It is not a weakly prime, because it can be changed into another prime (640808401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320404245 + 320404246.

It is an arithmetic number, because the mean of its divisors is an integer number (320404246).

Almost surely, 2^640808491 is an apocalyptic number.

640808491 is a deficient number, since it is larger than the sum of its proper divisors (1).

640808491 is an equidigital number, since it uses as much as digits as its factorization.

640808491 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 55296, while the sum is 40.

The square root of 640808491 is about 25314.1954444537. The cubic root of 640808491 is about 862.1366068671.

The spelling of 640808491 in words is "six hundred forty million, eight hundred eight thousand, four hundred ninety-one".