Extracting coefficients from generating functions in the browser

[Joao C]

Dear SeqFans,
I have put together a simple website where one can input a generating function and extract its coefficients: coefficients.net

This could be a fun feature to have in the OEIS: while on the sequence page, you can play around with the generating function. Add a term, change a term, see how the sequence changes.

The site makes use of an open source, MIT licensed library, "nerdamer-prime", which runs entirely in the browser, meaning it wouldn't put pressure on the OEIS servers (the caveat being that it's quite slow).

What do you think?

This is my first message in the SeqFan mailing list - my apologies if it should've gone somewhere else.

João

[Simon Plouffe]

I tried it, you can't do : 1/(exp(x)-1) which would you
back the Bernoulli numbers. 
That one too : exp(x)/(exp(2*x)-1) : cannot do. 

but it can do 1/cos(x) which gives the Euler numbers. 

something to fix ? 
Best regards, 
 Simon plouffe

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[Brendan]

Those two examples are excusable because they have 1/x terms.

However, x/(exp(x)-1) and x*exp(x)/(exp(2*x)-1) also fail.

It seems that denominators have to have constant terms.

A stark example is x/(x+x^2) which fails even though 1/(1+x) succeeds.

Brendan.

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