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%I #5 Nov 19 2021 07:18:51
%S 1,2,5,4,21,25,16,36,106,712,1588,3775,900,4356,18496,14400,45700,
%T 87003,135445,229543,554216,937019,1764724,3431952,3431088,10217808,
%U 21357233,36972202,42436276,79056144,235027304,261540000,530582544,705929608,1371526825,1127941321
%N a(n) is the least number k such that A349474(k) = n, or -1 if no such k exists.
%e a(3) = 5 since 5 is the least number k such that A349474(k) = 3.
%t cflen[n_] := Length @ ContinuedFraction[DivisorSigma[0, n] / DivisorSigma[-1, n]]; seq[len_, nmax_] := Module[{s = Table[0, {len}], c = 0, n = 1, i}, While[c < len && n < nmax, i = cflen[n]; If[i <= len && s[[i]] == 0, c++; s[[i]] = n]; n++]; TakeWhile[s, # > 0 &]]; seq[20, 10^7]
%Y Cf. A071865, A349473, A349474.
%K nonn
%O 1,2
%A _Amiram Eldar_, Nov 19 2021
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