A225941 - OEIS

%I #15 Sep 16 2019 10:10:39

%S 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,

%T 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,

%U 15,65,82,28,32,60,10,48,8,14,23,5,32,18,3,80,28,12,2

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

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

%H Pierre CAMI, <a href="/A225941/b225941.txt">Table of n, a(n) for n = 1..3000</a>

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

%o (PFGW & SCRIPTIFY)

%o SCRIPT

%o DIM n, 0

%o DIM k

%o DIMS t

%o OPENFILEOUT myf, a(n).txt

%o LABEL a

%o SET n, n+1

%o IF n>3000 THEN END

%o SET k, 0

%o LABEL b

%o SET k, k+1

%o SETS t, %d, %d\,; n; k

%o PRP k*6^n-1, t

%o IF ISPRP THEN GOTO c

%o GOTO b

%o LABEL c

%o WRITE myf, t

%o GOTO a

%o (PARI) a(n) = my(k=1); while (!isprime(k*6^n-1), k++); k; \\ _Michel Marcus_, Sep 16 2019

%Y Cf. A225911.

%K nonn

%O 1,2

%A _Pierre CAMI_, May 21 2013