640687 has 2 divisors, whose sum is σ = 640688. Its totient is φ = 640686.

The previous prime is 640669. The next prime is 640691. The reversal of 640687 is 786046.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640687 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320343 + 320344.

It is an arithmetic number, because the mean of its divisors is an integer number (320344).

2⁶⁴⁰⁶⁸⁷ is an apocalyptic number.

640687 is a deficient number, since it is larger than the sum of its proper divisors (1).

640687 is an equidigital number, since it uses as much as digits as its factorization.

640687 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8064, while the sum is 31.

The square root of 640687 is about 800.4292598350. The cubic root of 640687 is about 86.2082119211.

The spelling of 640687 in words is "six hundred forty thousand, six hundred eighty-seven".