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 A357944 #25 Oct 23 2022 11:59:37
%S A357944 0,1,2,5,33,8,15,22,28,25,35,65,69,78,123,165,180,97,105,203,115,294,
%T A357944 199,373,326,238,300,506,350,354,361,367,380,388,392,408,491,573,628,
%U A357944 498,502,509,513,516,744,615,683,763,1201,1072,906,1083,872,1100,1113,1364,1385,1438,1274,1387
%N A357944 If n appears in A357943, a(n) is the smallest k such that A357943(k) = n, otherwise a(n) = -1.
%H A357944 Scott R. Shannon, <a href="/A357944/b357944.txt">Table of n, a(n) for n = 0..10000</a>
%H A357944 Scott R. Shannon, <a href="/A357944/a357944.png">Image for the first 10000000 terms of A357943</a>.
%t A357944 nn = 1500; c[_] = q[_] = 0; Array[Set[{a[#], c[#], q[#]}, {#, 1, #}] &, 3, 0]; Do[(a[n] = c[#]; c[c[#]]++; If[q[c[#]] == 0, Set[q[c[#]], n]]) &[a[n - a[n - 1] - 1]], {n, 3, nn}]; {0}~Join~TakeWhile[Array[q, nn], # > 0 &] (* _Michael De Vlieger_, Oct 23 2022 *)
%Y A357944 Cf. A357943.
%K A357944 nonn
%O A357944 0,3
%A A357944 _Scott R. Shannon_, Oct 22 2022