%I #16 Sep 08 2022 08:45:21
%S 60,760,2440,5800,8680,17350,21840,27010,40030,84060,108010,109890,
%T 131110,222940,277750,309120,313030,334170,346140,348660,356500,
%U 358330,387160,419230,470880,553410,578820,604030,683340,729820,799890,801630
%N Numbers k such that 1*k + 1, 3*k + 1, 9*k + 1, 27*k + 1, 81*k + 1 are all primes.
%C A subsequence of A112041.
%t prQ[n_]:=Module[{ns=n*3^Range[0,4]+1},And@@PrimeQ[ns]]; Select[Range[ 810000],prQ] (* _Harvey P. Dale_, Jul 01 2012 *)
%o (Magma) [n: n in [1..1000000] |IsPrime(n+1) and IsPrime(3*n+1) and IsPrime(9*n+1) and IsPrime(27*n+1)and IsPrime(81*n+1)] // _Vincenzo Librandi_, Nov 13 2010
%Y Cf. A112041, A112043.
%K nonn
%O 1,1
%A _Pierre CAMI_, Aug 26 2005