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 A226429 #12 Jul 22 2017 09:16:15 %S A226429 2,3,4,4,5,7,8,9,8,9,11,13,11,15,16,14,14,18,20,21 %N A226429 Number of numerical semigroups S of genus 3^n having a minimal generating set of cardinality 2. %H A226429 Shalom Eliahou and Jorge Ramírez Alfonsín, <a href="http://www.math.univ-montp2.fr/~ramirez/semigroups.pdf">Two-generator numerical semigroups and Fermat and Mersenne numbers</a>, SIAM J. Discrete Math., 25(2), 2011, 622-630. %F A226429 a(n) = n + 1 if 2*3^n - 1 is prime. %F A226429 a(n) ~ n + 1. %Y A226429 Cf. A003307, A079363. %K A226429 nonn,more %O A226429 1,1 %A A226429 _Arkadiusz Wesolowski_, Jun 06 2013