639679 has 2 divisors, whose sum is σ = 639680. Its totient is φ = 639678.

The previous prime is 639677. The next prime is 639689. The reversal of 639679 is 976936.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 639679 - 2¹ = 639677 is a prime.

Together with 639677, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (639671) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319839 + 319840.

It is an arithmetic number, because the mean of its divisors is an integer number (319840).

2⁶³⁹⁶⁷⁹ is an apocalyptic number.

639679 is a deficient number, since it is larger than the sum of its proper divisors (1).

639679 is an equidigital number, since it uses as much as digits as its factorization.

639679 is an evil number, because the sum of its binary digits is even.

The product of its digits is 61236, while the sum is 40.

The square root of 639679 is about 799.7993498372. The cubic root of 639679 is about 86.1629774098.

The spelling of 639679 in words is "six hundred thirty-nine thousand, six hundred seventy-nine".