640637 has 4 divisors (see below), whose sum is σ = 642876. Its totient is φ = 638400.

The previous prime is 640631. The next prime is 640649. The reversal of 640637 is 736046.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 106276 + 534361 = 326^2 + 731^2 .

It is a cyclic number.

It is not a de Polignac number, because 640637 - 2⁴ = 640621 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640631) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 614 + ... + 1287.

It is an arithmetic number, because the mean of its divisors is an integer number (160719).

2⁶⁴⁰⁶³⁷ is an apocalyptic number.

It is an amenable number.

640637 is a deficient number, since it is larger than the sum of its proper divisors (2239).

640637 is a wasteful number, since it uses less digits than its factorization.

640637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2238.

The product of its (nonzero) digits is 3024, while the sum is 26.

The square root of 640637 is about 800.3980259846. The cubic root of 640637 is about 86.2059692645.

The spelling of 640637 in words is "six hundred forty thousand, six hundred thirty-seven".