639631 has 2 divisors, whose sum is σ = 639632. Its totient is φ = 639630.

The previous prime is 639601. The next prime is 639637. The reversal of 639631 is 136936.

639631 = 324² + 325² + ... + 329².

639631 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 639631 - 2⁵ = 639599 is a prime.

It is a super-2 number, since 2×639631² = 818255632322, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 639631.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (639637) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319815 + 319816.

It is an arithmetic number, because the mean of its divisors is an integer number (319816).

2⁶³⁹⁶³¹ is an apocalyptic number.

639631 is a deficient number, since it is larger than the sum of its proper divisors (1).

639631 is an equidigital number, since it uses as much as digits as its factorization.

639631 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2916, while the sum is 28.

The square root of 639631 is about 799.7693417480. The cubic root of 639631 is about 86.1608222005.

The spelling of 639631 in words is "six hundred thirty-nine thousand, six hundred thirty-one".