640420656 has 60 divisors (see below), whose sum is σ = 1695969576. Its totient is φ = 208240640.

The previous prime is 640420621. The next prime is 640420673. The reversal of 640420656 is 656024046.

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 11 ways as a sum of consecutive naturals, for example, 76720 + ... + 84656.

Almost surely, 2^640420656 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 640420656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (847984788).

640420656 is an abundant number, since it is smaller than the sum of its proper divisors (1055548920).

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

640420656 is a wasteful number, since it uses less digits than its factorization.

640420656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8030 (or 7983 counting only the distinct ones).

The product of its (nonzero) digits is 34560, while the sum is 33.

The square root of 640420656 is about 25306.5338598552. The cubic root of 640420656 is about 861.9626421365.

The spelling of 640420656 in words is "six hundred forty million, four hundred twenty thousand, six hundred fifty-six".