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 A086122 #15 May 25 2019 01:54:55
%S A086122 31,19531,12207031,305175781,177635683940025046467781066894531,
%T A086122 14693679385278593849609206715278070972733319459651094018859396328480215743184089660644531,
%U A086122 35032461608120426773093239582247903282006548546912894293926707097244777067146515037165954709053039550781
%N A086122 Primes of the form (5^k-1)/4.
%C A086122 Corresponding exponents k are listed in A004061. - _Alexander Adamchuk_, Jan 23 2007
%F A086122 a(n) = (5^A004061(n) - 1)/4 = A003463[ A004061(n) ]. - _Alexander Adamchuk_, Jan 23 2007
%F A086122 A003464 INTERSECT A000040.
%t A086122 Do[f=(5^n-1)/4;If[PrimeQ[f],Print[{n,f}]],{n,1,1000}] (* _Alexander Adamchuk_, Jan 23 2007 *)
%t A086122 Select[(5^Range[300]-1)/4,PrimeQ] (* _Harvey P. Dale_, Dec 11 2016 *)
%Y A086122 Cf. A000668, A076481.
%Y A086122 Cf. A003463, A004061, A074479.
%K A086122 nonn
%O A086122 1,1
%A A086122 _Labos Elemer_, Jul 23 2003
%E A086122 More terms from _Alexander Adamchuk_, Jan 23 2007