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 A343559 #19 Jul 01 2021 08:21:44
%S A343559 1,1,2,2,1,1,2,3,3,3,2,1,1,2,1,2,3,4,4,4,4,3,2,1,1,1,2,3,3,2,1,2,3,4,
%T A343559 5,5,5,5,5,4,3,2,1,1,1,1,2,3,4,4,4,3,2,2,3,1,2,3,4,5,6,6,6,6,6,6,5,4,
%U A343559 3,2,1,1,1,1,1,2,3,4,5,5,5,5,4,3,2,2,2,3,4,4,3
%N A343559 Irregular triangle read by rows: the n-th row gives the column indices of the consecutive elements of the spiral of the n X n matrix defined in A126224.
%H A343559 Stefano Spezia, <a href="/A343559/b343559.txt">First 30 rows of the triangle, flattened</a>
%e A343559 The triangle begins
%e A343559 1
%e A343559 1 2 2 1
%e A343559 1 2 3 3 3 2 1 1 2
%e A343559 1 2 3 4 4 4 4 3 2 1 1 1 2 3 3 2
%e A343559 ...
%t A343559 a:={};nmax:=6;For[n=1,n<=nmax,n++,For[s=1,s<=2n-1,s++,If[OddQ[s]&&Mod[s,4]==1 ,k=Floor[s/4];For[i=1,i<=Ceiling[n-s/2],i++,AppendTo[a,k+i]];k=+Floor[s/4]+Ceiling[n-s/2],If[EvenQ[s],For[i=1,i<=Ceiling[n-s/2],i++,AppendTo[a,k]],For[i=1,i<=Ceiling[n-s/2],i++,AppendTo[a,k-i]];k=k-i+1]]]]; a
%Y A343559 Cf. A000290 (row length), A002265, A002411 (row sums), A010873, A060747, A126224, A343558 (row indices).
%K A343559 nonn,look,tabf
%O A343559 1,3
%A A343559 _Stefano Spezia_, Apr 19 2021