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Least j such that P(n)#/2 + 2*P(j) is prime with j > 1 except j=1 for n=1.
1

%I #7 Mar 28 2015 22:39:46

%S 1,3,4,5,6,8,10,11,10,11,13,13,14,23,17,23,38,25,44,24,24,40,30,28,32,

%T 37,32,29,30,91,36,52,39,56,51,47,54,39,109,46,46,47,65,53,97,154,63,

%U 49,81,92,66,57,119,60,63,59,95,75,63,83,154,70,79,70,66,105,74,77,79,91

%N Least j such that P(n)#/2 + 2*P(j) is prime with j > 1 except j=1 for n=1.

%t Primorial[n_Integer] := Block[{k = Product[Prime[j], {j, n}]}, k]; f[n_] := Block[{p = Primorial[n]/2}, If[n == 1, j = 1, j = 2]; While[ !PrimeQ[p + 2Prime[j]], j++ ]; j]; Table[ f[n], {n, 70}] (* _Robert G. Wilson v_, Sep 04 2004 *)

%Y The P(j) sequence is given in A098170.

%K nonn

%O 1,2

%A _Pierre CAMI_, Aug 30 2004

%E Edited, corrected and extended by _Robert G. Wilson v_, Sep 04 2004