The first differences are 3, 5, 7, 9 and the second differences are 2.
Hence, the first term of the sequence is n^2 (since half of 2 is 1).
Subtracting n^2 from the sequence gives 3, 3, 3, 3, 3.
So putting these two terms together gives n^2 + 3.
hope this helpful :)
