杭电ACM2045题

#include<stdio.h> int main() { int n; while(scanf("%d",&n)!=EOF) { __int64 a[51]; int i; a[1]=3; a[2]=6; a[3]=6; for(i=4;i<=50;i++) { a[i]=a[i-1]+a[i-2]*2; } printf("%I64d\n",a

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