640656621 has 48 divisors (see below), whose sum is σ = 1059065280. Its totient is φ = 383771520.

The previous prime is 640656617. The next prime is 640656623. The reversal of 640656621 is 126656046.

It is a happy number.

640656621 is a `hidden beast` number, since 640 + 6 + 5 + 6 + 6 + 2 + 1 = 666.

It is not a de Polignac number, because 640656621 - 2² = 640656617 is a prime.

It is a super-2 number, since 2×640656621² = 820881812062275282, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640656623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 236551 + ... + 239243.

It is an arithmetic number, because the mean of its divisors is an integer number (22063860).

Almost surely, 2^640656621 is an apocalyptic number.

It is an amenable number.

640656621 is a deficient number, since it is larger than the sum of its proper divisors (418408659).

640656621 is a wasteful number, since it uses less digits than its factorization.

640656621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2808 (or 2796 counting only the distinct ones).

The product of its (nonzero) digits is 51840, while the sum is 36.

The square root of 640656621 is about 25311.1955663892. The cubic root of 640656621 is about 862.0684934171.

The spelling of 640656621 in words is "six hundred forty million, six hundred fifty-six thousand, six hundred twenty-one".