UVA 580

【题目分析】
计数类型的DP，巧妙 ，妙啊

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【代码】

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <cmath>using namespace std;long long a[501];long long d[501];int main(){    a[3]=7;a[4]=13;a[5]=24;    for (int i=6;i<=500;++i)        a[i]=a[i-1]+a[i-2]+a[i-3];    for (int i=3;i<=500;++i)        d[i]=pow(2,i*1.0)-a[i];    int n;    while (scanf("%d",&n)!=EOF&&n)        printf("%lld\n",d[n]);}