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 A266278 #42 Jan 05 2018 14:25:58 %S A266278 5,57,489,4125,35117,299681,2557605,21826045,186255781,1589441093, %T A266278 13563736693,115748216413,987755062201,8429158472781,71931509371765, %U A266278 613838505628281,5238284505542721,44701699729693429,381468772192258129,3255321946095461785,27779786302899765081 %N A266278 Number of legal Go positions on a 2 X n board. %H A266278 Colin Barker, <a href="/A266278/b266278.txt">Table of n, a(n) for n = 1..1000</a> %H A266278 John Tromp, <a href="http://tromp.github.io/go/L2.html">Number of legal 2xn Go positions</a> %H A266278 J. Tromp and G. Farnebäck, <a href="http://dx.doi.org/10.1007/978-3-540-75538-8_8">Combinatorics of Go</a>, Lecture Notes in Computer Science, 4630, 84-99, 2007. %H A266278 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (10,-16,31,-13,20,2,-1). %F A266278 a(n) = 10*a(n-1)-16*a(n-2)+31*a(n-3)-13*a(n-4)+20*a(n-5)+2*a(n-6)-a(n-7). %F A266278 G.f.: x*(1 + x)^2*(5 - 3*x - 5*x^3 - x^4) / ((1 + x^2)*(1 - 10*x + 15*x^2 - 21*x^3 - 2*x^4 + x^5)). - _Colin Barker_, Jan 05 2018 %e A266278 For n = 1, the a(1) = 5 legal 2 X 1 boards are .. X. O. .X .O %o A266278 (PARI) Vec(x*(1 + x)^2*(5 - 3*x - 5*x^3 - x^4) / ((1 + x^2)*(1 - 10*x + 15*x^2 - 21*x^3 - 2*x^4 + x^5)) + O(x^40)) \\ _Colin Barker_, Jan 05 2018 %Y A266278 Cf. A094777, A102620. %K A266278 nonn,easy %O A266278 1,1 %A A266278 _Felix Fröhlich_, Dec 26 2015 %E A266278 Corrected and edited by _John Tromp_, Jan 26 2016