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 A107639 #5 Mar 31 2012 13:22:04 %S A107639 5,7,31,11,5,3,809,661,139,73,521,701,131,487,89,211,733,3011,311, %T A107639 8837,2837,8831,1733,401,983,17881,1783,19553,13859 %N A107639 Smallest prime a such that (a*b)^2 + a*b -1 is prime with b prime = 2^(2*n) - 2^n - 1, see A098845 for n. %e A107639 2^4-2^2-1=3=b(1) prime, (3*3)^2+3*3-1=89 prime so a(1)=3 %e A107639 2^8-2^4-1=239=b(2) prime, (7*239)^2+7*239-1=2800601 prime so a(2)=7 %Y A107639 Cf. A098845. %K A107639 hard,more,nonn %O A107639 1,1 %A A107639 _Pierre CAMI_, Jun 10 2005