640825 has 6 divisors (see below), whose sum is σ = 794654. Its totient is φ = 512640.

The previous prime is 640793. The next prime is 640837. The reversal of 640825 is 528046.

It can be written as a sum of positive squares in 3 ways, for example, as 19881 + 620944 = 141^2 + 788^2 .

It is not a de Polignac number, because 640825 - 2⁵ = 640793 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (25), and also a Moran number because the ratio is a prime number: 25633 = 640825 / (6 + 4 + 0 + 8 + 2 + 5).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 640825.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 12792 + ... + 12841.

2⁶⁴⁰⁸²⁵ is an apocalyptic number.

It is an amenable number.

640825 is a deficient number, since it is larger than the sum of its proper divisors (153829).

640825 is a wasteful number, since it uses less digits than its factorization.

640825 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25643 (or 25638 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 25.

The square root of 640825 is about 800.5154589388. The cubic root of 640825 is about 86.2144010478.

The spelling of 640825 in words is "six hundred forty thousand, eight hundred twenty-five".