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A158019 Numbers such that (n-1)/2 and 10*n-1 are both prime.

%I A158019 #11 Dec 12 2024 20:51:11
%S A158019 11,15,23,27,35,39,83,107,123,143,167,179,195,203,207,227,255,275,279,
%T A158019 347,399,423,455,479,567,587,623,627,695,707,735,759,767,779,795,839,
%U A158019 843,863,867,935,975,983,1007,1043,1095,1115,1155,1215,1227,1283,1323
%N A158019 Numbers such that (n-1)/2 and 10*n-1 are both prime.
%C A158019 Relating the two prime types:
%C A158019 (p-1)/2,(p-1)/4,(p-1)/6,(p-1)/8,(p-1)/10,(p-1)/12...
%C A158019 and
%C A158019 2*p-1,4*p-1,6*p-1,8*p-1,10*p-1...
%C A158019 where both contain 11,23 subsequence.
%H A158019 Robert Israel, <a href="/A158019/b158019.txt">Table of n, a(n) for n = 1..10000</a>
%p A158019 filter:= proc(n) isprime((n-1)/2) and isprime(10*n-1) end proc:
%p A158019 select(filter, [seq(i,i=3..10000,4)]); # _Robert Israel_, Dec 12 2024
%t A158019 Flatten[Table[If[PrimeQ[(n - 1)/2] && PrimeQ[10*n - 1], n, {}], {n, 1, 10000}]]
%t A158019 Select[Range[1,1500,2], PrimeQ[(#-1)/2]&&PrimeQ[10#-1]&] (* _Harvey P. Dale_, Mar 10 2013 *)
%K A158019 nonn
%O A158019 1,1
%A A158019 _Roger L. Bagula_ and _Gary W. Adamson_, Mar 11 2009, Mar 20 2009