640631 has 2 divisors, whose sum is σ = 640632. Its totient is φ = 640630.

The previous prime is 640621. The next prime is 640649. The reversal of 640631 is 136046.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640631 is a prime.

It is a super-2 number, since 2×640631² = 820816156322, which contains 22 as substring.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320315 + 320316.

It is an arithmetic number, because the mean of its divisors is an integer number (320316).

2⁶⁴⁰⁶³¹ is an apocalyptic number.

640631 is a deficient number, since it is larger than the sum of its proper divisors (1).

640631 is an equidigital number, since it uses as much as digits as its factorization.

640631 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 432, while the sum is 20.

The square root of 640631 is about 800.3942778406. The cubic root of 640631 is about 86.2057001379.

Adding to 640631 its reverse (136046), we get a palindrome (776677).

The spelling of 640631 in words is "six hundred forty thousand, six hundred thirty-one".