10-19 AC

2013.cpp

@@ -0,0 +1,15 @@
+#include <iostream>
+#include <cmath>
+using namespace std;
+int main(){
+    // a1 = 1
+    // an = 2(an-1 + 1)
+    // an + 2 = 2(an-1 + 2)
+    // an + 2 = 3*2^(n-1)
+    // an = 3*2^(n-1) - 2
+    int x;
+    while (cin >> x){
+        cout << 3*(long long)pow(2,x-1)-2 << endl;
+    }
+    return 0;
+}