640644656544 has 48 divisors (see below), whose sum is σ = 1868546917440. Its totient is φ = 213548218560.

The previous prime is 640644656543. The next prime is 640644656557. The reversal of 640644656544 is 445656446046.

640644656544 is a `hidden beast` number, since 6 + 4 + 0 + 6 + 4 + 46 + 56 + 544 = 666.

It is a tau number, because it is divible by the number of its divisors (48).

It is a Harshad number since it is a multiple of its sum of digits (54).

It is not an unprimeable number, because it can be changed into a prime (640644656543) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 370742572 + ... + 370744299.

It is an arithmetic number, because the mean of its divisors is an integer number (38928060780).

Almost surely, 2^640644656544 is an apocalyptic number.

It is an amenable number.

640644656544 is an abundant number, since it is smaller than the sum of its proper divisors (1227902260896).

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

640644656544 is a wasteful number, since it uses less digits than its factorization.

640644656544 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 741486890 (or 741486876 counting only the distinct ones).

The product of its (nonzero) digits is 33177600, while the sum is 54.

The spelling of 640644656544 in words is "six hundred forty billion, six hundred forty-four million, six hundred fifty-six thousand, five hundred forty-four".