640081639 has 2 divisors, whose sum is σ = 640081640. Its totient is φ = 640081638.

The previous prime is 640081613. The next prime is 640081669. The reversal of 640081639 is 936180046.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640081639 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 640081598 and 640081607.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640081669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320040819 + 320040820.

It is an arithmetic number, because the mean of its divisors is an integer number (320040820).

Almost surely, 2^640081639 is an apocalyptic number.

640081639 is a deficient number, since it is larger than the sum of its proper divisors (1).

640081639 is an equidigital number, since it uses as much as digits as its factorization.

640081639 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 31104, while the sum is 37.

The square root of 640081639 is about 25299.8347623063. The cubic root of 640081639 is about 861.8105173493.

The spelling of 640081639 in words is "six hundred forty million, eighty-one thousand, six hundred thirty-nine".