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%I #16 Jan 14 2022 07:58:48
%S 1,4,15,30,42,360,196,525,2080,320,7168,123200,35200,150920,196000,
%T 1232000,61236,466560,106831872,49787136,14580000,155648000,94058496,
%U 123561984,47385000
%N Smallest k such that A349410(k) = n or -1 if no such number exists.
%t 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 Cf. A349410.
%Y Similar sequences: A005179, A348184.
%K nonn,more
%O 1,2
%A _Tejo Vrush_, Nov 17 2021
%E Escape clause value changed to -1. - _N. J. A. Sloane_, Jan 14 2022