-1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -

[N. J. A. Sloane]

Message from Dean H.:

From: Dean Hickerson <dean at line.math.ucdavis.edu>
To: eclark at math.usf.edu, njas at research.att.com, ogerard at ext.jussieu.fr
Subject: Subject: Re:  -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -

(I tried to send this to seqfan, but it got rejected; I don't know why.)

Edwin Clark wrote:

> Strangely enough this sequence does not seem to appear in the EIS.
> Is this an oversight on my part, or is it really missing?

Neil replied:

> Yes, I agree, it is missing from the OEIS
>
> Ed, will you kindly submit it?
...
> However, an equivalent sequence IS in the database
> - change -1's to 0's and you get A021913.

Also, the negative of the sequence is in the database:

%N A057077 Periodic sequence 1,1,-1,-1...; expansion of (1+x)/(1+x^2).

Dean Hickerson
dean at math.ucdavis.edu