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A231810 Numbers n such that p-1 does not divide n+1 for every prime divisor p of n. 2
1, 5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 49, 53, 59, 61, 65, 67, 71, 73, 79, 83, 85, 89, 91, 97, 101, 103, 107, 109, 113, 121, 125, 127, 131, 133, 137, 139, 145, 149, 151, 157, 163, 167, 169, 173, 179, 181, 185, 187, 191, 193, 197, 199, 205, 211 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

MATHEMATICA

fa = FactorInteger; Gu[n_] := Union@Table[IntegerQ[(n + 1)/(fa[n][[i, 1]] - 1)], {i, Length[fa[n]]}]; Select[Range[20000], Gu[#] == {False} &]

Join[{1}, Select[Range[2, 300], NoneTrue[(#+1)/(FactorInteger[#][[All, 1]]-1), IntegerQ]&]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Mar 08 2019 *)

PROG

(PARI) isok(n) = {my(f=factor(n)[, 1]); for (k=1, #f~, if (!((n+1) % (f[k]-1)), return(0)); ); return(1); } \\ Michel Marcus, Oct 02 2019

(MAGMA) [1] cat [k: k in [2..220]| #[p:p in PrimeDivisors(k)| IsIntegral((k+1)/(p-1))] eq 0]; // Marius A. Burtea, Oct 02 2019

CROSSREFS

Cf. A231811.

Sequence in context: A007310 A069040 A070191 * A314294 A290729 A314295

Adjacent sequences:  A231807 A231808 A231809 * A231811 A231812 A231813

KEYWORD

nonn

AUTHOR

José María Grau Ribas, Jan 20 2014

EXTENSIONS

Term 1 prepended by Max Alekseyev, Jan 20 2014

STATUS

approved

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Last modified May 27 13:56 EDT 2022. Contains 354097 sequences. (Running on oeis4.)