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A108200
Least positive k such that k*n + 1 is a golden semiprime (A108540).
1
5, 7, 62, 19, 1, 31, 2, 1254, 1692, 85, 912, 49, 20796, 1, 1234, 627, 50, 846, 4, 860, 28, 456, 4076, 418, 34, 10398, 564, 21, 91250, 617, 6, 47670, 304, 25, 6218, 423, 352018, 2, 6932, 430, 9348, 14, 400, 228, 2874, 2038, 324, 209, 12, 17, 5562, 5199, 25784, 282
OFFSET
1,1
COMMENTS
Conjecture: for every n > 4 there exists a number k < n^[n/2] such that k*n + 1 is a golden semiprime, where [] is the floor function.
LINKS
EXAMPLE
a(3) = 62 because 62*3+1 = 187 = 11*17 and 11*phi-17 = 0.7983... < 1.
MATHEMATICA
goldQ[n_] := Module[{f = FactorInteger[n]}, If[Length[f] != 2, False, If[Max[f[[;; , 2]]] != 1, False, Abs[f[[2, 1]] - f[[1, 1]] * GoldenRatio] < 1]]]; a[n_] := Module[{k = 1}, While[!goldQ[k * n + 1], k++]; k]; Array[a, 54] (* Amiram Eldar, Nov 29 2019 *)
CROSSREFS
Cf. A108540.
Sequence in context: A268433 A201109 A177336 * A077780 A307361 A260829
KEYWORD
nonn
AUTHOR
Jason Earls, Jun 15 2005
STATUS
approved