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 A098819 #13 Mar 01 2019 08:56:29
%S A098819 2,4,16,12,22,28,30,22,138,12,102,180,426,1444,9502,6568,2212,5380,
%T A098819 9942,3034,24222,31530,2962,7848,93280,3718
%N A098819 Least k such that k*(Mersenne_prime(n)^2) + 1 is prime.
%C A098819 Subsequence of A035092. - _Amiram Eldar_, Mar 01 2019
%e A098819 2*((2^2-1)^2)+1=19 prime so a(1)=2.
%t A098819 a[n_] := Module[{k = 1, m = (2^MersennePrimeExponent[n] - 1)^2}, While[! PrimeQ[k*m + 1], k++]; k]; Array[a, 20] (* _Amiram Eldar_, Mar 01 2019 *)
%Y A098819 Cf. A000043, A000668, A035092.
%K A098819 more,nonn
%O A098819 1,1
%A A098819 _Pierre CAMI_, Oct 08 2004
%E A098819 a(19)-a(22) from _Donovan Johnson_, Mar 23 2008
%E A098819 a(23)-a(26) from _Amiram Eldar_, Mar 01 2019