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 A131088 #13 Feb 26 2022 10:48:06 %S A131088 1,3,1,3,0,1,2,3,0,1,3,0,0,0,1,1,3,3,0,0,1,3,0,0,0,0,0,1,2,2,0,3,0,0, %T A131088 0,1,2,0,3,0,0,0,0,0,1,1,3,0,0,3,0,0,0,0,1,3,0,0,0,0,0,0,0,0,0,1,2,1, %U A131088 2,3,0,3,0,0,0,0,0,1,3,0,0,0,0,0,0,0,0,0,0,0,1 %N A131088 2*A051731 - A054525 as infinite lower triangular matrices. %C A131088 Row sums = A131089. %C A131088 A131090: (1, 3, 3, 2, 3, 1, 3, 2, 2, 1, ...) in every column interspersed with (k-1) zeros. %e A131088 First few rows of the triangle: %e A131088 1; %e A131088 3, 1; %e A131088 3, 0, 1; %e A131088 2, 3, 0, 1; %e A131088 3, 0, 0, 0, 1; %e A131088 1, 3, 3, 0, 0, 1 %e A131088 3, 0, 0, 0, 0, 0, 1; %e A131088 2, 2, 0, 3, 0, 0, 0, 1; %e A131088 ... %o A131088 (PARI) T(n,k) = 2*!(n%k) - if (!(n % k), moebius(n/k), 0); %o A131088 row(n) = vector(n, k, T(n,k)); %o A131088 lista(nn) = for (n=1, nn, v = row(n); for (k=1, #v, print1(v[k], ", "))); \\ _Michel Marcus_, Feb 26 2022 %Y A131088 Cf. A129979 (left border), A131089 (row sums), A051731, A054525. %K A131088 nonn,tabl %O A131088 1,2 %A A131088 _Gary W. Adamson_, Jun 14 2007 %E A131088 More terms from _Michel Marcus_, Feb 26 2022