638168645 has 4 divisors (see below), whose sum is σ = 765802380. Its totient is φ = 510534912.

The previous prime is 638168617. The next prime is 638168647. The reversal of 638168645 is 546861836.

It is a Cunningham number, because it is equal to 25262²+1.

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 229764964 + 408403681 = 15158^2 + 20209^2 .

It is a cyclic number.

It is not a de Polignac number, because 638168645 - 2⁶ = 638168581 is a prime.

It is a super-2 number, since 2×638168645² = 814518438922272050, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 638168645.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638168647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 63816860 + ... + 63816869.

It is an arithmetic number, because the mean of its divisors is an integer number (191450595).

Almost surely, 2^638168645 is an apocalyptic number.

It is an amenable number.

638168645 is a deficient number, since it is larger than the sum of its proper divisors (127633735).

638168645 is a wasteful number, since it uses less digits than its factorization.

638168645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 127633734.

The product of its digits is 829440, while the sum is 47.

The square root of 638168645 is about 25262.0000197926. Note that the first 4 decimals coincide. The cubic root of 638168645 is about 860.9511043235.

The spelling of 638168645 in words is "six hundred thirty-eight million, one hundred sixty-eight thousand, six hundred forty-five".