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 A121238 #10 Jul 13 2020 06:22:11 %S A121238 1,1,1,-1,1,1,-1,-1,1,1,1,-1,-1,1,-1,-1,1,1,1,-1,1,1,-1,-1,-1,1,1,-1, %T A121238 -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 A121238 a(n) = (-1)^(1+n+A088585(n)). %C A121238 Apparently the partial products of this sequence form the Hankel transform of A023359: 1, 1*1 = 1, 1*1*1 = 1, 1*1*1*-1 = -1, 1*1*1*-1*1 = -1, ... and 1, 1, 1, -1, -1, -1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1, -1, ... is the Hankel transform of A023359. %H A121238 <a href="/index/Fo#fold">Index entries for sequences obtained by enumerating foldings</a> %Y A121238 Cf. A023359, A088585. %K A121238 sign %O A121238 0,1 %A A121238 _Philippe Deléham_, Aug 21 2006