This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A280135 #26 Dec 27 2016 23:23:16 %S A280135 4,2,2,2,2,2,2,17,294,3,4,5,16,2,3,4,2,4,2,3,2,2,2,2,2,2,2,2,2,2,2,2, %T A280135 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, %U A280135 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2 %N A280135 Negative continued fraction of Pi (also called negative continued fraction expansion of Pi). %C A280135 Appears that these terms are related to continued fraction of Pi through simple transforms; original continued fraction terms X,1 -> negative continued fraction term X+2 (e.g., 15,1->17, and 292,1->294); other transforms are to be determined. %D A280135 Leonard Eugene Dickson, History of the Theory of Numbers, page 379. %e A280135 Pi = 4 - (1 / (2 - (1 / (2 - (1 / ...))))). %o A280135 (PARI) \p10000; p=Pi;for(i=1,300,print(i," ",ceil(p)); p=ceil(p)-p;p=1/p ) %Y A280135 Cf. A001203 (continued fraction of Pi). %Y A280135 Cf. A133593 (exact continued fraction of Pi). %Y A280135 Cf. A280136 (negative continued fraction of e). %K A280135 nonn %O A280135 1,1 %A A280135 _Randy L. Ekl_, Dec 26 2016