general term

General term is (n^2 - n + 2)/2.

2008-11-01 13:33:43 補充：
16 = 15 + 1 = 6 x 5/2 + 1
11 = 10 + 1 = 5 x 4/2 + 1
7 = 6 + 1 = 4 x 3/2 + 1
4 = 3 + 1 = 3 x 2/2 + 1
2 = 1 + 1 = 2 x 1/2 + 1
1 = 0 + 1 = 1 x 0/2 + 1

The n term is
Summation i=1 to n [Summation j=1 to j (j)]

2008-11-01 09:07:43 補充：
sorry, typo
Summation i=1 to n [Summation j=1 to i (j)]