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 A349428 #16 Jan 14 2022 07:58:48
%S A349428 1,4,15,30,42,360,196,525,2080,320,7168,123200,35200,150920,196000,
%T A349428 1232000,61236,466560,106831872,49787136,14580000,155648000,94058496,
%U A349428 123561984,47385000
%N A349428 Smallest k such that A349410(k) = n or -1 if no such number exists.
%t A349428 f[n_] := Module[{s = NestWhileList[n * DivisorSigma[0, #] &, 1, UnsameQ, All]}, Differences[Position[s, s[[-1]]]][[1, 1]]]; seq[len_, nmax_] := Module[{v = Table[0, {len}], n = 1, c = 0, i}, While[c < len && n < nmax, i = f[n]; If[i <= len && v[[i]] == 0, c++; v[[i]] = n]; n++]; TakeWhile[v, # > 0 &]]; seq[15, 10^6] (* _Amiram Eldar_, Nov 17 2021 *)
%Y A349428 Cf. A349410.
%Y A349428 Similar sequences: A005179, A348184.
%K A349428 nonn,more
%O A349428 1,2
%A A349428 _Tejo Vrush_, Nov 17 2021
%E A349428 Escape clause value changed to -1. - _N. J. A. Sloane_, Jan 14 2022