640690639 has 2 divisors, whose sum is σ = 640690640. Its totient is φ = 640690638.

The previous prime is 640690637. The next prime is 640690667. The reversal of 640690639 is 936096046.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 640690639 - 2¹ = 640690637 is a prime.

Together with 640690637, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 640690595 and 640690604.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640690637) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320345319 + 320345320.

It is an arithmetic number, because the mean of its divisors is an integer number (320345320).

Almost surely, 2^640690639 is an apocalyptic number.

640690639 is a deficient number, since it is larger than the sum of its proper divisors (1).

640690639 is an equidigital number, since it uses as much as digits as its factorization.

640690639 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 209952, while the sum is 43.

The square root of 640690639 is about 25311.8675525928. The cubic root of 640690639 is about 862.0837513707.

The spelling of 640690639 in words is "six hundred forty million, six hundred ninety thousand, six hundred thirty-nine".