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A200923 Least k such that (3^n - k)*3^n + 1 is a prime number. 5

%I

%S 1,1,7,1,3,1,7,5,9,29,19,1,7,49,49,9,23,1,3,29,53,39,41,35,7,5,51,33,

%T 3,81,83,15,21,31,61,69,67,87,27,5,19,55,153,35,99,31,23,49,47,95,3,

%U 115,89,55,23,61,139,49,87,5,153,87,269,113,67,207,41,33

%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=1},While[!PrimeQ[(c-k)*c+1],k++];k]; Array[lk,70] (* _Harvey P. Dale_, Jul 15 2017 *)

%Y Cf. A191617, A191618, A191619, A191620, A200920, A200921, A200922.

%K nonn

%O 1,3

%A _Michel Lagneau_, Nov 24 2011

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Last modified June 21 02:05 EDT 2021. Contains 345342 sequences. (Running on oeis4.)