640656 has 40 divisors (see below), whose sum is σ = 1840160. Its totient is φ = 213408.

The previous prime is 640649. The next prime is 640663. The reversal of 640656 is 656046.

640656 is a `hidden beast` number, since 6 + 4 + 0 + 656 = 666.

It is an interprime number because it is at equal distance from previous prime (640649) and next prime (640663).

It is a super-2 number, since 2×640656² = 820880220672, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640656.

It is an unprimeable number.

640656 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 310 + ... + 1173.

It is an arithmetic number, because the mean of its divisors is an integer number (46004).

2⁶⁴⁰⁶⁵⁶ is an apocalyptic number.

It is an amenable number.

640656 is an abundant number, since it is smaller than the sum of its proper divisors (1199504).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

640656 is a wasteful number, since it uses less digits than its factorization.

640656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1500 (or 1488 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 640656 is about 800.4098949913. The cubic root of 640656 is about 86.2068214878.

It can be divided in two parts, 640 and 656, that added together give a 4-th power (1296 = 6⁴).

The spelling of 640656 in words is "six hundred forty thousand, six hundred fifty-six".