%I A006664 M1871
%S A006664 1,1,2,8,46,322,2546,21870,199494,1904624,18846714,191955370,2002141126,
%T A006664 21303422480,230553207346,2531848587534,28159614749270,316713536035464,
%U A006664 3597509926531778,41225699113145888,476180721050626814,5539597373695447322,
               64863295574835126394,763984568163192551672,9047263176444565467566
%N A006664 Number of irreducible systems of meanders.
%D A006664 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A006664 V. I. Arnol'd, A branched covering of CP^2->S^4, hyperbolicity and projective 
               topology [ Russian ], Sibir. Mat. Zhurn., 29 (No. 2, 1988), 36-47 
               = Siberian Math. J., 29 (1988), 717-725.
%D A006664 S. K. Lando and A. K. Zvonkin "Plane and projective meanders", S\'{e}ries 
               Formelles et Combinatoire Alg\'{e}brique. Laboratoire Bordelais de 
               Recherche Informatique, Universit\'{e} Bordeaux I, 1991, pp. 287-303.
%D A006664 S. K. Lando and A. K. Zvonkin, "Meanders", Selecta Mathematica Sovietica 
               Vol. 11, Number 2, pp. 117-144, 1992.
%D A006664 S. K. Lando and A. K. Zvonkin, "Plane and projective meanders", Theoretical 
               Computer Science Vol. 117, pp. 227-241, 1993.
%F A006664 A(x^2)=S(x^2)#inv(x*S(x^2)) where # is functional composition, S(x) is 
               g.f. of A001246 (squares of Catalan numbers) and inv(.) is functional 
               inverse. A(x) consists of even-numbered terms of A(x^2), odd terms 
               of which are 0. - Doug McIlroy (doug(AT)cs.dartmouth.edu), Mar 22 
               2006
%Y A006664 Sequence in context: A144164 A003091 A119501 this_sequence A141117 A145844 
               A005840
%Y A006664 Adjacent sequences: A006661 A006662 A006663 this_sequence A006665 A006666 
               A006667
%K A006664 nonn,nice
%O A006664 0,3
%A A006664 N. J. A. Sloane (njas(AT)research.att.com), Simon Plouffe (simon.plouffe(AT)gmail.com)
%E A006664 More terms from Doug McIlroy (doug(AT)cs.dartmouth.edu), Mar 22 2006