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 A138060 #12 Jul 01 2023 09:16:56
%S A138060 1,1,2,1,2,3,1,2,3,4,1,2,3,4,1,1,2,3,4,1,1,2,1,2,3,4,1,1,2,1,2,3,1,2,
%T A138060 3,4,1,1,2,1,2,3,1,2,3,4,1,2,3,4,1,1,2,1,2,3,1,2,3,4,1,2,3,4,1,1,2,3,
%U A138060 4,1,1,2,1,2,3,1,2,3,4,1,2,3,4,1,1,2,3,4,1,1,2,1,2,3,4,1,1,2,1,2,3,1,2,3,4
%N A138060 Triangle read by rows: row 1 = {1}; for n>1, row n is obtained from row n-1 by applying the morphism 1->1,2; 2->3; 3->4; 4->1.
%e A138060 {1},
%e A138060 {1, 2},
%e A138060 {1, 2, 3},
%e A138060 {1, 2, 3, 4},
%e A138060 {1, 2, 3, 4, 1},
%e A138060 {1, 2, 3, 4, 1, 1, 2},
%e A138060 {1, 2, 3, 4, 1, 1, 2, 1, 2, 3},
%e A138060 {1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4},
%e A138060 {1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 1},
%e A138060 {1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 1, 1, 2, 3, 4, 1, 1, 2},
%e A138060 {1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 1, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3}
%t A138060 SubstitutionSystem[{1 -> {1, 2}, 2 -> {3}, 3 -> {4}, 4 -> {1}}, {1}, 10] // Flatten (* _Jean-François Alcover_, Jul 01 2023 *)
%Y A138060 Row sums are A138289. Rows converge to A138297.
%Y A138060 Cf. A103684.
%K A138060 nonn,tabf,easy
%O A138060 1,3
%A A138060 _Roger L. Bagula_, May 02 2008
%E A138060 Edited by _N. J. A. Sloane_, May 06 2008