1,2

Antti Karttunen, Table of n, a(n) for n = 1..16384

Index entries for sequences related to sigma(n)

a(11) = 6 because sigma(6) = sigma(11) = 12.

With[{nn = 76}, With[{s = Values@ PositionIndex@ Array[DivisorSigma[1, #] &, nn]}, Array[s[[FirstPosition[s, #][[1]], 1 ]] &, nn]]] (* Michael De Vlieger, Nov 16 2017 *)

(PARI) a(n) = {my(k = 1); while(sigma(k) != sigma(n), k++); k; }

Cf. A000203, A069822, A286603.

Sequence in context: A254596 A286603 A291751 * A048893 A330814 A305903

Adjacent sequences: A275984 A275985 A275986 * A275988 A275989 A275990

nonn

Altug Alkan, Aug 15 2016

approved