A283676 - OEIS

%I #9 Apr 11 2017 08:26:36

%S 0,1,9,15,47,89,357,537,697,1037,1257,1643,1723,1995,2333,2357,2863,

%T 3395,3593,4795,5187,5349,5469,5759,5859,6339,6573,8097,8653,8683,

%U 8773,8827,8947,10213,10609,10959,11407,12325,13365,14109,15549,18589,18639,19343

%N a(0)=0, then a(n) = smallest odd k > a(n-1) such that 6*k^prime(n)-1 is prime.

%H Pierre CAMI, <a href="/A283676/b283676.txt">Table of n, a(n) for n = 0..225</a>

%e 6*1^prime(1)-1 = 5 prime so a(1)=1, prime (2)=3, 6*3^3-1 = 161 composite, 6*5^3-1 = 749 composite, 6*7^3-1 = 2057 composite, 6*9^3-1 = 4373 prime so a(2) = 9.

%t a[0] = 0; a[n_] := a[n] = Module[{k = Boole[OddQ@ #] + # + 1 &@ a[n - 1]}, While[! PrimeQ[6*k^Prime[n] - 1], k += 2]; k]; Table[a@ n, {n, 0, 43}] (* _Michael De Vlieger_, Mar 15 2017 *)

%o (PARI) foddk(n, k) = {while (! isprime(6*k^prime(n)-1), k+=2); k;}

%o lista(nn) = {k = 1; for (n=1, nn, k = foddk(n, k); print1(k, ", "); k += 2;);} \\ _Michel Marcus_, Mar 18 2017

%K nonn

%O 0,3

%A _Pierre CAMI_, Mar 14 2017