A225941 Smallest k such that k*6^n-1 is prime

1, 2, 2, 2, 2, 3, 5, 13, 3, 19, 5, 2, 3, 28, 12, 2, 15, 19, 19, 20, 7, 13, 5, 3, 4, 2, 2, 7, 42, 7, 4, 7, 5, 34, 8, 2, 78, 13, 12, 2, 3, 24, 4, 12, 2, 37, 30, 5, 2, 28, 12, 2, 2, 35, 59, 58, 15, 65, 82, 28, 32, 60, 10, 48, 8, 14, 23, 5, 32, 18, 3, 80, 28, 12, 2

Offset

1,2

Comments

In average k~0.6*n and 0<k<8*n until a proof k may be >8*n

Links

Pierre CAMI, Table of n, a(n) for n = 1..3000

Mathematica

skp[n_]:=Module[{k=1, c=6^n}, While[!PrimeQ[k*c-1], k++]; k]; Array[skp, 80] (* Harvey P. Dale, Jul 22 2013 *)

Prog

(PFGW & SCRIPTIFY)
SCRIPT
DIM n, 0
DIM k
DIMS t
OPENFILEOUT myf, a(n).txt
LABEL a
SET n, n+1
IF n>3000 THEN END
SET k, 0
LABEL b
SET k, k+1
SETS t, %d, %d\,; n; k
PRP k*6^n-1, t
IF ISPRP THEN GOTO c
GOTO b
LABEL c
WRITE myf, t
GOTO a
(PARI) a(n) = my(k=1); while (!isprime(k*6^n-1), k++); k; \\ Michel Marcus, Sep 16 2019

Crossrefs

Cf. A225911.

Sequence in context: A356758 A098133 A138185 * A138705 A333528 A319187

Adjacent sequences: A225938 A225939 A225940 * A225942 A225943 A225944

Keyword

nonn

Author

Pierre CAMI, May 21 2013

Status

approved