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%I #11 May 24 2024 15:25:24
%S 5,5,5,7,5,5,5,7,5,5,5,11,5,5,5,7,5,5,5,7,5,5,5,11,5,5,5,7,5,5,5,7,5,
%T 5,5,11,5,5,5,7,5,5,5,7,5,5,13,11,5,5,5,7,5,5,5,7,5,5,11,17,7,5,5,7,5,
%U 5,5,7,5,5,5,11,7,5,5,7,5,5,7,7,11,5,5
%N Least prime p > 3 such that 2^n + p*2^k - 1 is prime for some k with n/3 < k < n+1.
%C The prime p seems to be < 31.
%H Pierre CAMI, <a href="/A205236/b205236.txt">Table of n, a(n) for n = 1..10800</a>
%e 2^1+5*2^1-1=11 prime so p=5 for n=1.
%e 2^2+5*2^2-1=23 prime so p=5 for n=2.
%e 2^3+5*2^3-1=47 prime so p=5 for n=3.
%o PFGW64 from Primeform group and SCRIPTIFY
%o Command : pfgw64 -f in.txt
%o in.txt file :
%o SCRIPT
%o DIM nn,0
%o DIM mm
%o DIM kk
%o DIMS tt
%o OPENFILEOUT myfile,prem.txt
%o LABEL loopn
%o SET nn,nn+1
%o IF nn>10800 THEN END
%o SET kk,2
%o LABEL loopk
%o SET kk,kk+1
%o SET mm,nn/3
%o LABEL loopm
%o SET mm,mm+1
%o IF mm>nn THEN GOTO loopk
%o SETS tt,%d,%d,%d\ ;nn;p(kk);mm
%o PRP 2^nn+p(kk)*2^mm-1,tt
%o IF ISPRIME THEN GOTO a
%o IF ISPRP THEN GOTO a
%o GOTO loopm
%o LABEL a
%o WRITE myfile,tt
%o GOTO loopn
%Y Cf. A205237.
%K nonn,changed
%O 1,1
%A _Pierre CAMI_, Jan 24 2012
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