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 A098555 #8 Mar 29 2015 19:07:28
%S A098555 1,2,2,6,2,14,2,90,18,80,230,80,354,84,84,1782,450,828,2562,2502,6882,
%T A098555 9288,890,16022,11088,31034,7272,92372
%N A098555 Least k such that k*Mersenne-prime(n)-1 is prime.
%t A098555 mexp = {the list in A000043}; f[n_] := Block[{k = 2, mp = 2^mexp[[n]] - 1}, While[ !PrimeQ[mp*k - 1] && k < 10000, k++ ]; If[k == 10000, 0, k]]; Do[ Print[ f[n]], {n, 22}] (* _Robert G. Wilson v_, Sep 17 2004 *)
%Y A098555 Cf. A000043, A000668, A098556.
%K A098555 hard,nonn
%O A098555 1,2
%A A098555 _Pierre CAMI_, Sep 14 2004
%E A098555 More terms from _Pierre CAMI_, Jan 17 2005
%E A098555 a(1)=1, a(23)=890, a(27)=7272 corrected, other terms through a(28)=92372 verified by _Ray Chandler_, Apr 16 2009