%I A030449
%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="Sindx_Se.html#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.
%Y A030449 Sequence in context: A003460 A157626 A128120 this_sequence A120277 A015086 
               A052466
%Y A030449 Adjacent sequences: A030446 A030447 A030448 this_sequence A030450 A030451 
               A030452
%K A030449 nonn
%O A030449 1,2
%A A030449 marcel_j(AT)hilbert.maths.utas.edu.au (Marcel Jackson)