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 A159905 #4 Jun 02 2025 01:38:56 %S A159905 1,1,1,2,2,1,2,2,2,1,4,4,3,2,1,2,2,3,3,2,1,6,6,5,4,3,2,1,4,4,4,4,4,3, %T A159905 2,1,6,6,6,6,5,4,3,2,1,4,4,5,5,5,5,4,3,2,1,10,10,9,8,7,6,5,4,3,2,1,4, %U A159905 4,4,5,6,6,6,5,4,3,2,1 %N A159905 Triangle read by rows, Mobius transform of A004736. %C A159905 Row sums = A007438, Mobius transform of the triangular numbers. %C A159905 Left border = phi(n), A000010. %F A159905 Triangle read by rows, A054525 * A004736. A054525 = the Mobius transform, A004736 = the natural number "decrescendo" triangle: (1; 2,1; 3,2,1;...) %e A159905 First few rows of the triangle = %e A159905 1; %e A159905 1, 1; %e A159905 2, 2, 1; %e A159905 2, 2, 2, 1; %e A159905 4, 4, 3, 2, 1; %e A159905 2, 2, 3, 3, 2, 1; %e A159905 6, 6, 5, 4, 3, 2, 1; %e A159905 4, 4, 4, 4, 4, 3, 2, 1; %e A159905 6, 6, 6, 6, 5, 4, 3, 2, 1; %e A159905 4, 4, 5, 5, 5, 5, 4, 3, 2, 1; %e A159905 ... %Y A159905 Cf. A007438 %K A159905 nonn,tabl %O A159905 1,4 %A A159905 _Gary W. Adamson_, Apr 25 2009