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 A291971 #17 Sep 07 2017 06:14:15 %S A291971 1,0,3,0,3,0,3,9,0,3,9,0,3,18,0,3,18,27,0,3,27,27,0,3,27,54,0,3,36,81, %T A291971 0,3,36,108,81,0,3,45,135,81,0,3,45,189,162,0,3,54,216,243,0,3,54,270, %U A291971 405,0,3,63,324,486,243,0,3,63,378,729,243,0,3,72,432,891 %N A291971 Triangle read by rows: T(n,k) = 3 * T(n-k,k-1) + T(n-k,k) with T(0,0) = 1 for 0 <= k <= A003056(n). %H A291971 Seiichi Manyama, <a href="/A291971/b291971.txt">Rows n = 0..481, flattened</a> %e A291971 First few rows are: %e A291971 1; %e A291971 0, 3; %e A291971 0, 3; %e A291971 0, 3, 9; %e A291971 0, 3, 9; %e A291971 0, 3, 18; %e A291971 0, 3, 18, 27; %e A291971 0, 3, 27, 27; %e A291971 0, 3, 27, 54; %e A291971 0, 3, 36, 81; %e A291971 0, 3, 36, 108, 81. %Y A291971 Row sums give A032308. %Y A291971 Columns 0-1 give A000007, A010701. %Y A291971 Cf. A008289 (m=1), A291970 (m=2), this sequence (m=3). %K A291971 nonn,tabf,look %O A291971 0,3 %A A291971 _Seiichi Manyama_, Sep 07 2017