A349475 a(n) is the least number k such that A349474(k) = n, or -1 if no such k exists.

1, 2, 5, 4, 21, 25, 16, 36, 106, 712, 1588, 3775, 900, 4356, 18496, 14400, 45700, 87003, 135445, 229543, 554216, 937019, 1764724, 3431952, 3431088, 10217808, 21357233, 36972202, 42436276, 79056144, 235027304, 261540000, 530582544, 705929608, 1371526825, 1127941321

Offset: 1

Author

Amiram Eldar, Nov 19 2021

Keywords

• nonn

Examples

			a(3) = 5 since 5 is the least number k such that A349474(k) = 3.
		

Crossrefs

Cf. A071865, A349473, A349474.

Programs

Mathematica

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]