638776681 has 4 divisors (see below), whose sum is σ = 641083012. Its totient is φ = 636470352.

The previous prime is 638776673. The next prime is 638776729. The reversal of 638776681 is 186677836.

638776681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 202635225 + 436141456 = 14235^2 + 20884^2 .

It is a cyclic number.

It is not a de Polignac number, because 638776681 - 2³ = 638776673 is a prime.

It is a super-2 number, since 2×638776681² = 816071296378751522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (638774681) 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, 1152750 + ... + 1153303.

It is an arithmetic number, because the mean of its divisors is an integer number (160270753).

Almost surely, 2^638776681 is an apocalyptic number.

It is an amenable number.

638776681 is a deficient number, since it is larger than the sum of its proper divisors (2306331).

638776681 is a wasteful number, since it uses less digits than its factorization.

638776681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2306330.

The product of its digits is 2032128, while the sum is 52.

The square root of 638776681 is about 25274.0317519782. The cubic root of 638776681 is about 861.2244506146.

The spelling of 638776681 in words is "six hundred thirty-eight million, seven hundred seventy-six thousand, six hundred eighty-one".