638991081 has 12 divisors (see below), whose sum is σ = 923776308. Its totient is φ = 425629824.

The previous prime is 638991061. The next prime is 638991097. The reversal of 638991081 is 180199836.

638991081 is a `hidden beast` number, since 638 + 9 + 9 + 1 + 0 + 8 + 1 = 666.

638991081 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 2 ways, for example, as 98010000 + 540981081 = 9900^2 + 23259^2 .

It is a de Polignac number, because none of the positive numbers 2^k-638991081 is a prime.

It is a super-2 number, since 2×638991081² = 816619203195097122, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (638991011) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 19020 + ... + 40493.

It is an arithmetic number, because the mean of its divisors is an integer number (76981359).

Almost surely, 2^638991081 is an apocalyptic number.

It is an amenable number.

638991081 is a deficient number, since it is larger than the sum of its proper divisors (284785227).

638991081 is a wasteful number, since it uses less digits than its factorization.

638991081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 60712 (or 60709 counting only the distinct ones).

The product of its (nonzero) digits is 93312, while the sum is 45.

The square root of 638991081 is about 25278.2729038200. The cubic root of 638991081 is about 861.3207940750.

It can be divided in two parts, 63899 and 1081, that added together give a triangular number (64980 = T₃₆₀).

The spelling of 638991081 in words is "six hundred thirty-eight million, nine hundred ninety-one thousand, eighty-one".