Find showing all the work,the formula for the nth term of sequence 2,5,10,17,26

original, then difference, then difference of difference

2
...... 3
5 ........... 2
.......5
10 .......... 2
.......7
17 ...........2
.......9
26
constant difference of differences is parabola
well, y = x^2 + 1 works
an = n^2+1