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 A215055 Smallest k>0 such that 2*k*3^n-1 and 3^n-2*k are both prime and n>1 1
 1, 2, 4, 2, 14, 17, 5, 37, 10, 10, 29, 25, 110, 125, 55, 143, 28, 10, 277, 37, 5, 67, 14, 800, 241, 68, 551, 53, 133, 142, 61, 203, 131, 742, 245, 235, 5, 152, 20, 70, 248, 730, 382, 562, 199, 158, 199, 157, 236, 545, 334, 100, 5, 913, 782, 205, 809, 85, 106, 995 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 COMMENTS 3^n-2*k is the greatest prime q such that 9^n-q*3^n-1 is prime = 2*k*3^n-1 LINKS Pierre CAMI, Table of n, a(n) for n = 2..500 MATHEMATICA sk[n_]:=Module[{k=1, n3=3^n}, While[!PrimeQ[2k*n3-1]||!PrimeQ[n3-2k], k++]; k]; Array[sk, 70, 2] (* Harvey P. Dale, Oct 04 2016 *) PROG PFGW and SCRIPTIFY SCRIPT DIM nn, 1 DIM kk DIMS tt OPENFILEOUT myfile, a(n).txt LABEL loopn SET nn, nn+1 SET kk, 0 LABEL loopk SET kk, kk+1 SETS tt, %d, %d\ ; nn; kk PRP 2*kk*3^nn-1, tt IF ISPRP THEN GOTO a IF ISPRIME THEN GOTO a GOTO loopk LABEL a PRP 3^nn-2*kk, tt IF ISPRP THEN GOTO b IF ISPRIME THEN GOTO b GOTO loopk LABEL b WRITE myfile, tt GOTO loopn CROSSREFS Sequence in context: A062867 A264027 A113539 * A152877 A071353 A134763 Adjacent sequences:  A215052 A215053 A215054 * A215056 A215057 A215058 KEYWORD nonn AUTHOR Pierre CAMI, Aug 01 2012 STATUS approved

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Last modified June 22 21:29 EDT 2021. Contains 345393 sequences. (Running on oeis4.)