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A200921 Least k such that (3^n + k)*3^n - 1 is a prime number. 5

%I

%S 1,1,3,3,13,9,15,3,1,13,29,1,5,53,25,9,23,1,69,13,3,3,17,1,5,117,5,13,

%T 45,51,3,11,31,73,49,43,11,83,93,277,171,383,39,11,3,31,55,61,61,13,

%U 73,107,65,137,53,39,467,53,233,277,17,53,109,177,151,97,13

%N Least k such that (3^n + k)*3^n - 1 is a prime number.

%t Table[k = 0; While[!PrimeQ[(3^n + k)*3^n - 1], k++]; k, {n, 72}]

%t lk[n_]:=Module[{c=3^n,k=0},While[!PrimeQ[(c+k)c-1],k++];k]; Array[lk,70] (* _Harvey P. Dale_, Aug 19 2015 *)

%Y Cf. A191617, A191618, A191619, A191620, A200920, A200922, A200923.

%K nonn

%O 1,3

%A _Michel Lagneau_, Nov 24 2011

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Last modified July 26 11:35 EDT 2021. Contains 346294 sequences. (Running on oeis4.)