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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

F. Harary and R. C. Read, The enumeration of tree-like polyhexes, Proc. Edinb. Math. Soc. (2) 17 (1970), 1-13.

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

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: A183933 A056884 A006749 * A099949 A006231 A069007

Adjacent sequences:  A002210 A002211 A002212 * A002214 A002215 A002216

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Edited by Emeric Deutsch, Feb 18 2004

STATUS

approved

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Last modified April 19 03:59 EDT 2014. Contains 240738 sequences.