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 A002213 Number of polyhexes rooted at a hexagon and containing n hexagons. (Formerly M3907 N1603) 2
 1, 1, 5, 20, 84, 354, 1540, 6704, 29610, 131745, 591049, 2669346, 12131148, 55431285, 254539897, 1174027598, 5436826110, 25269402555, 117838870833, 551192276450, 2585418254532, 12158383558066, 57313008207960 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 REFERENCES 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 T. D. Noe, Table of n, a(n) for n = 1..200 F. Harary and R. C. Read, The enumeration of tree-like polyhexes, Proc. Edinburgh Math. Soc. (2) 17 (1970), 1-13. FORMULA G.f.: x+xU(x)+(3/2)xU(x)^2+(1/2)xU(x^2)+(1/3)xU(x)^3+(2/3)xU(x^3), where U(x)=[1-3x-sqrt((1-x)(1-5x))]/(2x). a(n) ~ 5^(n+1/2)/(2*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, Aug 13 2013 CROSSREFS Sequence in context: A270322 A056884 A006749 * A099949 A006231 A069007 Adjacent sequences:  A002210 A002211 A002212 * A002214 A002215 A002216 KEYWORD nonn,easy AUTHOR EXTENSIONS Edited by Emeric Deutsch, Feb 18 2004 STATUS approved

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Last modified September 21 23:55 EDT 2019. Contains 327286 sequences. (Running on oeis4.)