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A351169
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a(n) is the minimum number of vertices of degree 4 over all 4-collapsible graphs with n vertices.
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2
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5, 4, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 10, 10, 10, 10, 11, 11, 11, 12, 12, 12, 12, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 16, 16, 16, 16, 17, 17, 17, 18, 18, 18, 18, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 22, 22, 22
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OFFSET
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5,1
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COMMENTS
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A graph G is k-collapsible if it has minimum degree k and has no proper induced subgraph with minimum degree k.
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LINKS
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FORMULA
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a(n) = ceiling(2*n/7) for n > 7.
G.f.: x^5*(5 - x - x^2 + x^6 - 5*x^7 + x^8 + x^9 + x^10)/((1 - x)^2*(1 + x + x^2 + x^3 + x^4 + x^5 + x^6)). - Stefano Spezia, Feb 05 2022
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EXAMPLE
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A complete graph with 5 vertices is 4-collapsible with 5 degree 4 vertices.
The graph formed by removing two nonadjacent edges from a complete graph with 6 vertices is 4-collapsible with 4 degree 4 vertices.
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MATHEMATICA
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A351169[n_]:=If[n<8, 10-n, Ceiling[2n/7]];
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PROG
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(Python)
print([5, 4, 3] + [1+(2*n-1)//7 for n in range(8, 80)]) # Gennady Eremin, Mar 07 2022
(PARI) a(n) = if(n<8, 10-n, (2*n+6)\7); \\ Kevin Ryde, Mar 08 2022
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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