640517 has 4 divisors (see below), whose sum is σ = 643500. Its totient is φ = 637536.

The previous prime is 640499. The next prime is 640529. The reversal of 640517 is 715046.

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 101761 + 538756 = 319^2 + 734^2 .

It is a cyclic number.

It is not a de Polignac number, because 640517 - 2⁸ = 640261 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 640492 and 640501.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640517.

It is not an unprimeable number, because it can be changed into a prime (642517) 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, 1142 + ... + 1607.

It is an arithmetic number, because the mean of its divisors is an integer number (160875).

2⁶⁴⁰⁵¹⁷ is an apocalyptic number.

It is an amenable number.

640517 is a deficient number, since it is larger than the sum of its proper divisors (2983).

640517 is a wasteful number, since it uses less digits than its factorization.

640517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2982.

The product of its (nonzero) digits is 840, while the sum is 23.

The square root of 640517 is about 800.3230597702. The cubic root of 640517 is about 86.2005864126.

Subtracting 640517 from its reverse (715046), we obtain a square (74529 = 273²).

The spelling of 640517 in words is "six hundred forty thousand, five hundred seventeen".