递推+猜结论?（也不算猜的
#include <algorithm> #include <iostream> #include <cstring> #include <cstdio> #include <cctype> using namespace std; inline void read(long long &x) { int k = 1; x = 0; char c = getchar(); while (!isdigit(c)) if (c == '-') k = - 1, c = getchar(); else c = getchar(); while (isdigit(c)) x = (x << 1) + (x << 3) + (c ^ 48), c = getchar(); x *= k; } long long T, n, cm, dp[10101]; int main() { read(T); for (int plk = 1; plk <= T; ++plk) { read(n); memset(dp, 0, sizeof(dp)); dp[0] = 0, dp[1] = 2; cm = 5; for (int i = 2; i <= n; ++i) dp[i] = dp[i - 1] + cm, cm += 4; printf("%lld\n", dp[n]); } return 0; }