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 A189808 #8 May 03 2018 07:02:34 %S A189808 28,94,200,342,524,732,972,1236,1524,1840,2180,2544,2932,3344,3780, %T A189808 4240,4724,5232,5764,6320,6900,7504,8132,8784,9460,10160,10884,11632, %U A189808 12404,13200,14020,14864,15732,16624,17540,18480,19444,20432,21444,22480,23540 %N A189808 Number of right triangles on a (n+1) X 4 grid. %C A189808 Column 3 of A189814. %H A189808 R. H. Hardin, <a href="/A189808/b189808.txt">Table of n, a(n) for n = 1..200</a> %F A189808 Empirical: a(n) = 12*n^2 + 88*n - 240 for n>8. %F A189808 Conjectures from _Colin Barker_, May 03 2018: (Start) %F A189808 G.f.: 2*x*(14 + 5*x + x^2 - 2*x^3 + 2*x^4 - 7*x^5 + 3*x^6 - 4*x^7 + 2*x^9 - 2*x^10) / (1 - x)^3. %F A189808 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>8. %F A189808 (End) %e A189808 Some solutions for n=3: %e A189808 ..3..1....2..2....0..0....2..1....2..0....3..3....1..1....1..1....3..2....1..1 %e A189808 ..0..1....3..1....0..3....2..2....0..0....0..3....1..2....0..2....2..2....2..0 %e A189808 ..3..2....3..3....2..0....4..1....2..3....3..0....4..1....3..3....3..3....3..3 %Y A189808 Cf. A189814. %K A189808 nonn %O A189808 1,1 %A A189808 _R. H. Hardin_, Apr 28 2011