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 A000673 Number of bicentered 3-valent (or boron, or binary) trees with n nodes. (Formerly M0355 N0133) 3
 0, 0, 1, 0, 1, 1, 2, 2, 6, 8, 18, 30, 67, 127, 275, 551, 1192, 2507, 5475, 11820, 26007, 57077, 126686, 281625, 630660, 1416116, 3195784, 7232624, 16430563, 37429146, 85528079, 195940960, 450074270, 1036226173, 2391193488, 5529420585 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,7 REFERENCES A. Cayley, On the analytical forms called trees, with application to the theory of chemical combinations, Reports British Assoc. Advance. Sci. 45 (1875), 257-305 = Math. Papers, Vol. 9, 427-460 (see p. 451). R. C. Read, personal communication. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS E. M. Rains and N. J. A. Sloane, On Cayley's Enumeration of Alkanes (or 4-Valent Trees)., J. Integer Sequences, Vol. 2 (1999), Article 99.1.1. CROSSREFS A000672 = A000673 + A000675. Cf. A000022, A000200, A000602. Sequence in context: A136513 A214932 A054153 * A129383 A052957 A197465 Adjacent sequences:  A000670 A000671 A000672 * A000674 A000675 A000676 KEYWORD nonn,easy,nice AUTHOR STATUS approved

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