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 A071103 #12 Mar 07 2016 04:40:08 %S A071103 12,168,4224,206848,20316160,4053794816,1651951796224, %T A071103 1376451119022080,2342575493674434560,8125862822063095414784, %U A071103 57307393009149041432330240 %N A071103 Number of perfect matchings in variant of n X n+2 Aztec rectangle graph. %C A071103 The graph consists of the vertices (x,y) bounded by 0<=x<=2n+1, 0<=y<=2n+1, n+1<=x+y<=3n+1 and |y-x|<=n+2. Vertices (x1,y1) and (x2,y2) are adjacent iff |x1-x2|=1 and y1=y2 or x1=x2 and |y1-y2|=1 or |x1-x2|=|y1-y2|=1 and x1+y1+n is odd. The graph is planar, has A090288(n) vertices and 6*n^2 + 12*n + 1 edges. Figure 12 in the J. Propp reference shows the graph for n=3. - _Andrew Howroyd_, Mar 06 2016 %D A071103 J. Propp, Enumeration of matchings: problems and progress, pp. 255-291 in L. J. Billera et al., eds, New Perspectives in Algebraic Combinatorics, Cambridge, 1999 (see Problem 28). %H A071103 J. Propp, <a href="http://faculty.uml.edu/jpropp/update.pdf">Updated article</a> %H A071103 J. Propp, Enumeration of matchings: problems and progress, in L. J. Billera et al. (eds.), <a href="http://www.msri.org/publications/books/Book38/contents.html">New Perspectives in Algebraic Combinatorics</a> %K A071103 nonn %O A071103 1,1 %A A071103 _N. J. A. Sloane_, May 28 2002 %E A071103 a(4) inserted, a(6)-a(11) from _Andrew Howroyd_, Mar 06 2016