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 A245945 #11 Nov 05 2018 06:33:59 %S A245945 71,197,545,1501,4145,11441,31577,87161,240581,664051,1832917,5059221, %T A245945 13964475,38544783,106391413,293661867,810566283,2237327253, %U A245945 6175476757,17045567707,47049222251,129865390965,358454804639,989407924729 %N A245945 Number of length n+3 0..2 arrays with some pair in every consecutive four terms totalling exactly 2. %H A245945 R. H. Hardin, <a href="/A245945/b245945.txt">Table of n, a(n) for n = 1..210</a> %F A245945 Empirical: a(n) = 2*a(n-1) + 2*a(n-2) + a(n-3) - a(n-4) - 2*a(n-5) - 2*a(n-6) - a(n-7) + a(n-8) + a(n-9). %F A245945 Empirical g.f.: x*(71 + 55*x + 9*x^2 - 54*x^3 - 73*x^4 - 57*x^5 - 15*x^6 + 36*x^7 + 27*x^8) / ((1 - x)*(1 - x - 3*x^2 - 4*x^3 - 3*x^4 - x^5 + x^6 + 2*x^7 + x^8)). - _Colin Barker_, Nov 05 2018 %e A245945 Some solutions for n=8: %e A245945 ..0....1....1....1....2....1....0....0....1....1....2....1....0....0....1....2 %e A245945 ..1....1....2....1....0....2....2....1....0....2....0....0....0....1....1....0 %e A245945 ..2....2....0....2....1....0....2....0....2....2....0....1....2....1....0....0 %e A245945 ..0....1....0....0....1....1....0....2....0....1....2....2....0....0....1....1 %e A245945 ..1....2....1....1....1....0....2....1....0....0....2....1....1....2....1....2 %e A245945 ..0....1....1....0....1....1....2....0....1....1....0....0....0....2....1....1 %e A245945 ..2....2....1....2....2....1....1....0....1....2....2....1....1....1....2....0 %e A245945 ..2....0....1....2....1....0....0....1....0....2....0....0....2....0....1....2 %e A245945 ..0....1....0....0....2....0....1....1....0....0....2....2....0....2....2....0 %e A245945 ..0....1....1....1....0....2....1....2....2....2....2....1....2....0....1....0 %e A245945 ..2....2....1....1....0....2....2....1....2....1....1....0....0....0....2....2 %Y A245945 Column 2 of A245950. %K A245945 nonn %O A245945 1,1 %A A245945 _R. H. Hardin_, Aug 08 2014