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A006926
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Number of connected trivalent graphs with 2n nodes and girth exactly 6.
(Formerly M3969)
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12
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1, 1, 5, 32, 385, 7573, 181224, 4624480, 122089998, 3328899586, 93988909755
(list; graph; refs; listen; history; internal format)
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OFFSET
| 7,3
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REFERENCES
| CRC Handbook of Combinatorial Designs, 1996, p. 647.
Gordon Royle, personal communication.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| Jason Kimberley, Index of sequences counting connected k-regular simple graphs with girth exactly g
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FORMULA
| a(n) = A014374(n) - A014375(n).
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CROSSREFS
| Connected 3-regular simple graphs with girth exactly g: A198303 (triangle); specified g: A006923 (g=3), A006924 (g=4), A006925 (g=5), this sequence (g=6), A006927 (g=7).
Connected 3-regular simple graphs with girth at least g: A185131 (triangle); A002851 (g=3), A014371 (g=4), A014372 (g=5), A014374 (g=6), A014375 (g=7), A014376 (g=8).
Sequence in context: A093448 A094653 A135250 * A014374 A185336 A125709
Adjacent sequences: A006923 A006924 A006925 * A006927 A006928 A006929
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KEYWORD
| nonn,hard,more,changed
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| Definition corrected to include "connected", and "girth at least 6" minus "girth at least 7" formula provided by Jason Kimberley, Dec 12 2009
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