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 A030449 #10 Jun 13 2012 21:04:25
%S A030449 1,6,159,332380,2751884514765,272622932796281408879065986,
%T A030449 3641839910835401567626683593436003894250931310990279691
%N A030449 Number of elements in the free band (idempotent semigroup) on n generators.
%C A030449 An idempotent semigroup satisfies the equation xx=x for any element x.
%D A030449 J. Howie, Fundamentals of Semigroup Theory, Oxford University Press 1995, p. 123.
%H A030449 <a href="/index/Se#semigroups">Index entries for sequences related to semigroups</a>
%F A030449 a(n) = Sum_{k=1..n} C(n, k) A030450(k).
%Y A030449 Cf. A030450. A005345(n)=a(n)+1.
%K A030449 nonn
%O A030449 1,2
%A A030449 marcel_j(AT)hilbert.maths.utas.edu.au (Marcel Jackson)