640778544 has 120 divisors (see below), whose sum is σ = 2063037600. Its totient is φ = 181868544.

The previous prime is 640778513. The next prime is 640778581. The reversal of 640778544 is 445877046.

It is a self number, because there is not a number n which added to its sum of digits gives 640778544.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 156232 + ... + 160280.

It is an arithmetic number, because the mean of its divisors is an integer number (17191980).

Almost surely, 2^640778544 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 640778544, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1031518800).

640778544 is an abundant number, since it is smaller than the sum of its proper divisors (1422259056).

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

640778544 is a wasteful number, since it uses less digits than its factorization.

640778544 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4227 (or 4218 counting only the distinct ones).

The product of its (nonzero) digits is 752640, while the sum is 45.

The square root of 640778544 is about 25313.6039314832. The cubic root of 640778544 is about 862.1231765378.

The spelling of 640778544 in words is "six hundred forty million, seven hundred seventy-eight thousand, five hundred forty-four".