A342659 - OEIS

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

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OFFSET

1,1

LINKS

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

FORMULA

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

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 *)

CROSSREFS

Cf. A007691, A053669.

Cf. also A134740, A342658, A342660.

Sequence in context: A243061 A242911 A112486 * A253924 A141410 A333811

Adjacent sequences: A342656 A342657 A342658 * A342660 A342661 A342662

KEYWORD

nonn

AUTHOR

Antti Karttunen, Mar 19 2021

STATUS

approved