640658 has 4 divisors (see below), whose sum is σ = 960990. Its totient is φ = 320328.

The previous prime is 640649. The next prime is 640663. The reversal of 640658 is 856046.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 856046 = 2 ⋅428023.

It can be written as a sum of positive squares in only one way, i.e., 458329 + 182329 = 677^2 + 427^2 .

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 640658.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 160163 + ... + 160166.

2⁶⁴⁰⁶⁵⁸ is an apocalyptic number.

640658 is a deficient number, since it is larger than the sum of its proper divisors (320332).

640658 is a wasteful number, since it uses less digits than its factorization.

640658 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 320331.

The product of its (nonzero) digits is 5760, while the sum is 29.

The square root of 640658 is about 800.4111443502. The cubic root of 640658 is about 86.2069111945.

The spelling of 640658 in words is "six hundred forty thousand, six hundred fifty-eight".