1286 Necklace of Beads

Necklace of Beads
Time Limit: 1000MS
 
Memory Limit: 10000K
Total Submissions: 3389
 
Accepted: 1417
Description
Beads of red, blue or green colors are connected together into a circular necklace of n beads ( n < 24 ). If the repetitions that are produced by rotation around the center of the circular necklace or reflection to the axis of symmetry are all neglected, how many different forms of the necklace are there?
Input
The input has several lines, and each line contains the input data n.
-1 denotes the end of the input file.
Output
The output should contain the output data: Number of different forms, in each line correspondent to the input data.
Sample Input
4
5
-1

Sample Output
21
39

Source
Xi'an 2002
#include #include using namespace std; typedef long long int64; int64 gcd(int64 a, int64 b) { if (b) return gcd(b, a % b); else return a; } int main() { int64 n, i; double m; while(cin>>n) { m=3; if(n==-1) break; if(n==0) { printf("0/n"); continue; } int64 ans = 0; for (i = 1; i <= n; i++) ans += (int64)pow( m, (int)gcd(n, i) );//m^gcd(n,i) if (n & 1) ans += (int64)(pow(m, (int)(n + 1)/2) * n); else { ans += (int64)(pow(m, (int)n/2) * (n/2)); ans += (int64)(pow(m, (int)(n + 2)/2) * (n/2)); } ans/= (2 * n); cout<

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