640331999 has 2 divisors, whose sum is σ = 640332000. Its totient is φ = 640331998.

The previous prime is 640331981. The next prime is 640332073. The reversal of 640331999 is 999133046.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640331999 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 (640331899) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320165999 + 320166000.

It is an arithmetic number, because the mean of its divisors is an integer number (320166000).

Almost surely, 2^640331999 is an apocalyptic number.

640331999 is a deficient number, since it is larger than the sum of its proper divisors (1).

640331999 is an equidigital number, since it uses as much as digits as its factorization.

640331999 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 157464, while the sum is 44.

The square root of 640331999 is about 25304.7821369796. The cubic root of 640331999 is about 861.9228648704.

The spelling of 640331999 in words is "six hundred forty million, three hundred thirty-one thousand, nine hundred ninety-nine".