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 A133107 #7 Mar 08 2015 21:00:51 %S A133107 1,7,32,121,410,1294,3888,11273,31826,88041,239734,644758,1717191, %T A133107 4538129,11919760,31156313,81125827,210604604,545462798,1410226551, %U A133107 3641097828,9391872711,24208902420,62373915102,160663604377 %N A133107 Number of Ferrers diagrams with a single strictly smaller Ferrers puncture with the same orientation removed from the top with half-perimeter = n. %H A133107 Arvind Ayyer, Sep 11 2007, <a href="/A133107/b133107.txt">Table of n, a(n) for n = 6..76</a> %F A133107 G.f.: x^2*(-1 + 3*x - x^2 + (5*x^4 - 6*x^3 + 11*x^2 - 6*x + 1 + 4*x^6 - 12*x^5)^(1/2))/(2*(x^2 - 3*x + 1)*(1-2*x)^2) %e A133107 The sequence starts with n=6 because the smallest such object whose illustration is below has a perimeter of 12. (1 denotes cell inside the Ferrers diagram.) %e A133107 1 1 %e A133107 111 %Y A133107 Cf. A057410, A057406, A133106. %K A133107 easy,nonn %O A133107 6,2 %A A133107 _Arvind Ayyer_, Sep 11 2007