638784656 has 20 divisors (see below), whose sum is σ = 1310448492. Its totient is φ = 300604416.

The previous prime is 638784649. The next prime is 638784659. The reversal of 638784656 is 656487836.

It can be written as a sum of positive squares in 2 ways, for example, as 575040400 + 63744256 = 23980^2 + 7984^2 .

It is a junction number, because it is equal to n+sod(n) for n = 638784598 and 638784607.

It is not an unprimeable number, because it can be changed into a prime (638784659) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1173965 + ... + 1174508.

Almost surely, 2^638784656 is an apocalyptic number.

It is an amenable number.

638784656 is an abundant number, since it is smaller than the sum of its proper divisors (671663836).

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

638784656 is a wasteful number, since it uses less digits than its factorization.

638784656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2348498 (or 2348492 counting only the distinct ones).

The product of its digits is 5806080, while the sum is 53.

The square root of 638784656 is about 25274.1895221192. The cubic root of 638784656 is about 861.2280346717.

The spelling of 638784656 in words is "six hundred thirty-eight million, seven hundred eighty-four thousand, six hundred fifty-six".