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Least k such that 4*n*k-1 is a prime.
1

%I #7 May 18 2013 16:49:19

%S 1,1,1,2,1,1,3,1,2,2,1,1,2,3,1,2,1,1,2,1,1,3,4,2,2,1,1,2,3,2,5,1,1,2,

%T 1,3,3,1,2,3,1,1,5,7,1,2,3,1,3,1,5,5,1,2,2,1,1,2,13,1,2,3,1,5,4,1,6,1,

%U 3,3,1,3,5,3,2,2,1,1,2,4,2,3,1,7,3,3,1,5,4,1,2,1,2,2,1,1,3,4,3,5,6,3,2,4

%N Least k such that 4*n*k-1 is a prime.

%H Harvey P. Dale, <a href="/A037034/b037034.txt">Table of n, a(n) for n = 1..1000</a>

%e a(5)=1 because 4*5*1-1=19 is a prime

%t lk[n_]:=Module[{c=4n,k=1},While[!PrimeQ[c*k-1],k++];k]; Array[lk,110] (* _Harvey P. Dale_, Jun 05 2012 *)

%Y Cf. A016014.

%K nonn

%O 1,4

%A _Felice Russo_

%E More terms from _Erich Friedman_