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 A143971 #12 Jul 22 2025 06:11:20 %S A143971 1,4,1,7,4,1,10,7,4,1,13,10,7,4,1,16,13,10,7,4,1,19,16,13,10,7,4,1,22, %T A143971 19,16,13,10,7,4,1,25,22,19,16,13,10,7,4,1,28,25,22,19,16,13,10,7,4,1, %U A143971 31,28,25,22,19,16,13,10,7,4,1 %N A143971 Triangle read by rows, (3n-2) subsequences decrescendo. %C A143971 Row sums = pentagonal numbers, A000326: (1, 5, 12, 22, 35,...). %C A143971 The alternating row sums lead to A032766 and the antidiagonal sums to A006578. - _Johannes W. Meijer_, Sep 05 2013 %F A143971 Triangle read by rows, (3n-2) subsequences decrescendo; 1<=k<=n. %F A143971 (1, 4, 7, 10, 13,...) in every column. %F A143971 T(n,k) = 3*n - 3*k + 1. %e A143971 Triangle starts %e A143971 1; %e A143971 4, 1; %e A143971 7, 4, 1; %e A143971 10, 7, 4, 1; %e A143971 ... %p A143971 T := (n, k) -> 3*n-3*k+1: seq(seq(T(n, k), k=1..n), n=1..11); # _Johannes W. Meijer_, Sep 05 2013 %Y A143971 Cf. A016777, A000326, A209634. %K A143971 nonn,tabl %O A143971 1,2 %A A143971 _Gary W. Adamson_, Sep 06 2008 %E A143971 Terms a(17) and a(38) corrected and terms added by _Johannes W. Meijer_, Sep 05 2013