This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A138025 #18 Jul 09 2025 23:32:54 %S A138025 19099919,52554569,85864769,171729539,198479579,226366139,305192579, %T A138025 344319029,396959159,474118349,574964129,610385159,685066979, %U A138025 764406059,1085182229,1126004219,1195651139,1372213439,1484454269,1573750049,2270291519,2365144079,2400025739 %N A138025 Numbers that remain prime through 7 iterations of function f(x) = 2x + 1. %C A138025 n, 2*n+1, 4*n+3, 8*n+7, 16*n+15, 32*n+31, 64*n+63, and 128*n+127 are primes. - _John Cerkan_, Dec 04 2016 %F A138025 a(n) == 29 (mod 30). - _John Cerkan_, Nov 30 2016 %t A138025 Select[Prime[Range[10^7]],PrimeQ[a1=2*#+1]&&PrimeQ[a2=2*a1+1]&&PrimeQ[a3=2*a2+1]&&PrimeQ[a4=2*a3+1]&&PrimeQ[a5=2*a4+1]&&PrimeQ[a6=2*a5+1]&&PrimeQ[a7=2*a6+1] &] %K A138025 nonn %O A138025 1,1 %A A138025 _Vladimir Joseph Stephan Orlovsky_, May 01 2008 %E A138025 More terms from _Vladimir Joseph Stephan Orlovsky_, Jan 17 2009 %E A138025 a(7)-a(23) from _John Cerkan_, Nov 30 2016