Here is another general formula:
(You can simplify that if you like, but about all you can do is factor out .
How I got the 2nd solution was to find the average of the two solutions for even
and odd terms in my first answer above to be . Then I found the
common distance from the average for each solution to be . Then I
knew that this common distance gets added to the average when is +1,
and this common distance gets subtracted from the average when is -1.
Edwin
