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 A349946 #5 Dec 15 2021 02:28:43
%S A349946 2,3,4,3,4,5,5,6,4,5,6,6,7,7,8,5,6,7,7,8,8,9,9,10,6,7,8,8,9,9,10,10,
%T A349946 11,11,12,7,8,9,9,10,10,11,11,12,12,13,13,14,8,9,10,10,11,11,12,12,13,
%U A349946 13,14,14,15,15,16,9,10,11,11,12,12,13,13,14,14,15
%N A349946 a(n) = A349526(n) + A349526(n+1).
%C A349946 Every positive integer n >= 2 occurs exactly n-1 times; the last occurrence of n is a((n-1)^2).
%e A349946 A349426 = (1,1,2,2,1,3,2,3,3,1,4,2,4,3,4,4,1,...), in which every pair i,j of positive integers occurs exactly once; a(1) = 1+1, a(2) = 1+2, a(3) = 2+2.
%t A349946 t = {1, 1}; Do[t = Join[t, Riffle[Range[n], n], {n}], {n, 2, 100}];
%t A349946 u = Flatten[Partition[t, 2]];
%t A349946 v = Table[n (n + 1), {n, 1, 80}];
%t A349946 d = Delete[u, Map[{#} &, v]]; (* A349526 *)
%t A349946 p = Table[{d[[n]], d[[n + 1]]}, {n, 1, 150}];
%t A349946 Map[Total, p] (* A349946 *)
%Y A349946 Cf. A349526, A349947 (array: row n shows positions of n+1 in A349946).
%K A349946 nonn
%O A349946 1,1
%A A349946 _Clark Kimberling_, Dec 07 2021