%I A006343 M3400
%S A006343 1,0,1,1,4,4,10,34,112,398,1443,5387,20482,79177,310102,1228187,4910413,
%T A006343 19792582,80343445,328159601,1347699906,5561774999,23052871229,
%U A006343 95926831442,400587408251,1678251696379,7051768702245,29710764875014
%N A006343 Arkons: number of elementary maps with n-1 nodes.
%D A006343 K. Appel and W. Haken, Every planar map is four colorable. With the collaboration 
               of J. Koch. Contemporary Mathematics, 98. American Mathematical Society, 
               Providence, RI, 1989. xvi+741 pp. ISBN: 0-8218-5103-9.
%D A006343 F. R. Bernhart, Topics in Graph Theory Related to the Five Color Conjecture. 
               Ph.D. Dissertation, Kansas State Univ., 1974.
%D A006343 F. R. Bernhart, Catalan, Motzkin and Riordan numbers, Discr. Math., 204 
               (1999) 73-112.
%D A006343 G. D. Birkhoff and D. C. Lewis, Chromatic polynomials. Trans. Amer. Math. 
               Soc. 60, (1946). 355-451.
%D A006343 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%F A006343 a(n-1) = Sum (n-k-1)^(-1)*binomial(n, k)*binomial(2*n-3*k-4, n-2*k-2); 
               k = 0..[ (n-2)/2 ], n >= 3.
%Y A006343 Cf. A000934.
%Y A006343 Sequence in context: A095009 A145598 A117881 this_sequence A161433 A107856 
               A128499
%Y A006343 Adjacent sequences: A006340 A006341 A006342 this_sequence A006344 A006345 
               A006346
%K A006343 easy,nonn,nice
%O A006343 0,5
%A A006343 N. J. A. Sloane (njas(AT)research.att.com).