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A037915
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Floor[(3n + 4)/4]
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6
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1, 1, 2, 3, 4, 4, 5, 6, 7, 7, 8, 9, 10, 10, 11, 12, 13, 13, 14, 15, 16, 16, 17, 18, 19, 19, 20, 21, 22, 22, 23, 24, 25, 25, 26, 27, 28, 28, 29, 30, 31, 31, 32, 33, 34, 34, 35, 36, 37, 37, 38, 39, 40, 40, 41, 42, 43, 43, 44, 45, 46, 46, 47, 48, 49, 49, 50, 51, 52, 52, 53, 54, 55
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| a(n-1) is the "cover index" guaranteed by a multigraph with minimum degree n. I.e., in a multigraph where every node has degree >=n, it contains a(n-1) disjoint edge covers (sets of edges touching every vertex), and this is tight. [From David Pritchard (daveagp(AT)alum.mit.edu), May 07 2010]
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REFERENCES
| R. Gupta, On the chromatic index and the cover index of a multigraph, Lecture Notes in Mathematics Volume 642, Springer, 1978, pages 204-215. doi:10.1007/BFb0070378 [From David Pritchard (daveagp(AT)alum.mit.edu), May 07 2010]
N. Alon et al., Polychromatic Colorings of Plane Graphs, Discrete and Computational Geometry 42 (2009), 421-442. doi:10.1007/s00454-009-9171-5 [From David Pritchard (daveagp(AT)alum.mit.edu), May 07 2010]
L. Andersen, Lower bounds on the cover-index of a graph, Discrete Mathematics 25 (1979), 199-210. doi:10.1016/0012-365X(79)90076-1 [From David Pritchard (daveagp(AT)alum.mit.edu), May 07 2010]
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LINKS
| John A. Pelesko, Generalizing the Conway-Hofstadter $10,000 Sequence, Journal of Integer Sequences, Vol. 7 (2004), Article 04.3.5.
A nice open-access proof that a(n-1) disjoint edge covers exist is given in Alon et al. (2009), who rediscovered the result. [From David Pritchard (daveagp(AT)alum.mit.edu), May 07 2010]
Index to sequences with linear recurrences with constant coefficients, signature (1,0,0,1,-1).
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FORMULA
| G.f.: (1+x^2+x^3)/((1-x)*(1-x^4)).
(1/8) {6n + 5 + (-1)^n - 2(-1)^[(n-1)/2] }. - Ralf Stephan, Jun 10 2005
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EXAMPLE
| E.g. every multigraph with minimum degree 7 contains a(7-1)=5 disjoint edge covers. This is tight for a 3-vertex graph: e.g. the multigraph with V = {a, b, c} and E = {4*ab, 4*bc, 3*ac} has minimum degree 7 does not have >5 disjoint edge covers. [From David Pritchard (daveagp(AT)alum.mit.edu), May 07 2010]
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MATHEMATICA
| Table[ Floor[(3n + 4)/4], {n, 1, 75} ]
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CROSSREFS
| Sequence in context: A025528 A123580 A072894 * A195180 A069210 A195172
Adjacent sequences: A037912 A037913 A037914 * A037916 A037917 A037918
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 06 2002
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