638818640 has 40 divisors (see below), whose sum is σ = 1488520800. Its totient is φ = 254965376.

The previous prime is 638818619. The next prime is 638818651. The reversal of 638818640 is 46818836.

It is a tau number, because it is divible by the number of its divisors (40).

It is a super-2 number, since 2×638818640² = 816178509622899200, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 638818591 and 638818600.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 28811 + ... + 45909.

It is an arithmetic number, because the mean of its divisors is an integer number (37213020).

Almost surely, 2^638818640 is an apocalyptic number.

It is an amenable number.

638818640 is an abundant number, since it is smaller than the sum of its proper divisors (849702160).

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

638818640 is a wasteful number, since it uses less digits than its factorization.

638818640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17579 (or 17573 counting only the distinct ones).

The product of its (nonzero) digits is 221184, while the sum is 44.

The square root of 638818640 is about 25274.8618196025. The cubic root of 638818640 is about 861.2433071397.

The spelling of 638818640 in words is "six hundred thirty-eight million, eight hundred eighteen thousand, six hundred forty".