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From: "John D'Errico" <woodchips@rochester.rr.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: nth term
Date: Mon, 25 Feb 2008 22:22:02 +0000 (UTC)
Organization: John D'Errico (1-3LEW5R)
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"Mark Mortlock" <arty_guitarist@yahoo.co.uk> wrote in message 
<fpv7u2$1us$1@fred.mathworks.com>...
> 1   1   1   1   1    1    1    1
> -   -   -   -   -    -    -    -
> 3   12  30  60  105  168  252  360
> 
> The third series of fractions above are worked out using the
> formula n(n+1)/2-n.I need to finish off the series of
> fractions up to the ninth series. I am stuggling to find the
> formula for the fourth series of fractions and beyond.

What have you tried?

What does diff tell you about that series?
How about higher order differences? What
order polynomial is necessary to represent
these terms exactly?

John