hdu 1465不容易系列

#include <stdio.h> int main() { int n,i; __int64 a[21]; a[1] = 0; a[2] = 1; for(i = 3;i <= 20;i ++) { a[i] = (a[i-1] + a[i-2]) * (i-1); } while(scanf("%d",&n) != EOF) { printf("%I64d\n",a[n]); } return 0; }