Another way:
datax = Range[7];
datay = {3, 7, 14, 24, 37, 53, 72};
data = Transpose[{datax, datay}];
FindFormula[data, n, 1] // Rationalize
(* 2 - n/2 + (3 n^2)/2 *)
datax = Range[10];
datay = {1, 2, 21, 76, 185, 366, 637, 1016, 1521, 2170};
data = Transpose[{datax, datay}];
FindFormula[data, n, 1] // Rationalize
(* 7 n - 9 n^2 + 3 n^3 *)
Regards,MI
