640665220 has 96 divisors (see below), whose sum is σ = 1512354816. Its totient is φ = 226368000.

The previous prime is 640665209. The next prime is 640665239. The reversal of 640665220 is 22566046.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 813667 + ... + 814453.

It is an arithmetic number, because the mean of its divisors is an integer number (15753696).

Almost surely, 2^640665220 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 640665220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (756177408).

640665220 is an abundant number, since it is smaller than the sum of its proper divisors (871689596).

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

640665220 is a wasteful number, since it uses less digits than its factorization.

640665220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 941 (or 939 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 31.

The square root of 640665220 is about 25311.3654313630. The cubic root of 640665220 is about 862.0723503422.

The spelling of 640665220 in words is "six hundred forty million, six hundred sixty-five thousand, two hundred twenty".