640945 has 4 divisors (see below), whose sum is σ = 769140. Its totient is φ = 512752.

The previous prime is 640943. The next prime is 640949. The reversal of 640945 is 549046.

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 505521 + 135424 = 711^2 + 368^2 .

It is a cyclic number.

It is not a de Polignac number, because 640945 - 2¹ = 640943 is a prime.

It is not an unprimeable number, because it can be changed into a prime (640943) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 64090 + ... + 64099.

It is an arithmetic number, because the mean of its divisors is an integer number (192285).

2⁶⁴⁰⁹⁴⁵ is an apocalyptic number.

It is an amenable number.

640945 is a deficient number, since it is larger than the sum of its proper divisors (128195).

640945 is a wasteful number, since it uses less digits than its factorization.

640945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128194.

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 640945 is about 800.5904071371. The cubic root of 640945 is about 86.2197821750.

The spelling of 640945 in words is "six hundred forty thousand, nine hundred forty-five".