638507681 has 6 divisors (see below), whose sum is σ = 742753890. Its totient is φ = 547292256.

The previous prime is 638507677. The next prime is 638507689. The reversal of 638507681 is 186705836.

It can be written as a sum of positive squares in only one way, i.e., 628003600 + 10504081 = 25060^2 + 3241^2 .

It is not a de Polignac number, because 638507681 - 2² = 638507677 is a prime.

It is a super-2 number, since 2×638507681² = 815384117391995522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (638507689) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 6515336 + ... + 6515433.

It is an arithmetic number, because the mean of its divisors is an integer number (123792315).

Almost surely, 2^638507681 is an apocalyptic number.

It is an amenable number.

638507681 is a deficient number, since it is larger than the sum of its proper divisors (104246209).

638507681 is a wasteful number, since it uses less digits than its factorization.

638507681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13030783 (or 13030776 counting only the distinct ones).

The product of its (nonzero) digits is 241920, while the sum is 44.

The square root of 638507681 is about 25268.7095238360. The cubic root of 638507681 is about 861.1035414290.

The spelling of 638507681 in words is "six hundred thirty-eight million, five hundred seven thousand, six hundred eighty-one".