A342659 The least prime that does not divide the n-th multiply perfect number: a(n) = A053669(A007691(n)).

2, 5, 3, 7, 3, 5, 3, 11, 11, 5, 11, 7, 3, 7, 5, 3, 11, 5, 3, 13, 11, 7, 3, 7, 3, 11, 5, 11, 5, 13, 11, 5, 11, 11, 7, 7, 5, 13, 5, 5, 3, 11, 5, 11, 23, 11, 11, 11, 11, 11, 11, 23, 11, 13, 7, 13, 23, 11, 5, 5, 13, 5, 11, 5, 17, 17, 17, 17, 17, 17, 17, 17, 13, 17, 17, 11, 19, 11, 23, 19, 11, 5, 7, 11, 5, 7, 17, 17, 7, 7, 5

Offset: 1

Author

Antti Karttunen, Mar 19 2021

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1600

Crossrefs

Cf. A007691, A053669.

Cf. also A134740, A342658, A342660.

Programs

Mathematica

Map[Block[{k = 1}, While[Mod[#, Prime[k]] == 0, k++]; Prime[k]] &, Select[Range[10^6], IntegerQ@ DivisorSigma[-1, #] &] ] (* or, using the b-file at A007691: *)
Map[Block[{k = 1}, While[Mod[#, Prime[k]] == 0, k++]; Prime[k]] &, DeleteCases[Import["https://oeis.org/A007691/b007691.txt", "Data"], ?(Length@ # == 0 &)][[1 ;; 91, -1]] ] (* _Michael De Vlieger, Mar 19 2021 *)

Formula

a(n) = A053669(A007691(n)).