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 A194090 #8 Mar 31 2012 10:22:49
%S A194090 1,1,1,3,8,35,172,1121,8017,63213
%N A194090 The number of biconnected squaregraphs of perimeter 2*n.
%C A194090 The CWEB program squaregraph.w cited below relates a(n) to the number of certain partitions of {1,2,...,2*n} into n pairs.
%D A194090 See A194088
%H A194090 Don Knuth, <a href="http://www-cs-faculty.stanford.edu/~knuth/programs/squaregraph.w">squaregraph.w</a> (CWEB program).
%e A194090 For n=4 the a(4)=3 cases of perimeter 8 are the two trominoes and the square tetromino.
%o A194090 (CWEB) (see Knuth link).
%Y A194090 A194088, A194089, A194091, A194092, A194093.
%K A194090 nonn,hard,more
%O A194090 1,4
%A A194090 _Don Knuth_, Aug 15 2011