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A103300
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Number of perfect rulers with length n.
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30
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1, 1, 1, 2, 3, 4, 2, 12, 8, 4, 38, 30, 14, 6, 130, 80, 32, 12, 500, 326, 150, 66, 18, 4, 944, 460, 166, 56, 12, 6, 2036, 890, 304, 120, 20, 10, 2, 2678, 974, 362, 100, 36, 4, 2, 4892, 2114, 684, 238, 68, 22, 4, 16318, 6350, 2286, 836, 330, 108, 24, 12, 31980, 12252
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OFFSET
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0,4
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COMMENTS
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For definitions, references and links related to complete rulers see A103294.
The values for n = 208-213 are 22,0,0,0,4,4 according to Arch D. Robison. The values for 199-207 are not yet known. - Peter Luschny, Feb 20 2014, Jun 28 2019
Zero values at 135, 136, 149, 150, 151, 164, 165, 166, 179, 180, 181, 195, 196, 209, 210, 211. - Ed Pegg Jr, Jun 23 2019 [These values were found by Arch D. Robison, see links. Peter Luschny, Jun 28 2019]
Zero values at 135, 136, 149, 150, 151, 164, 165, 166, 179, 180, 181, 195, 196 have been replaced with correct values using an additional mark.
A lower bound for 209 is 62, for 210 is 16, and for 211 is 204.
The verified value for 212 and for 213 is 4. (End)
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LINKS
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FORMULA
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EXAMPLE
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a(5)=4 counts the perfect rulers with length 5, {[0,1,3,5],[0,2,4,5],[0,1,2,5],[0,3,4,5]}.
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CROSSREFS
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Cf. A004137 (Maximal number of edges in a graceful graph on n nodes).
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KEYWORD
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hard,nonn,nice
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AUTHOR
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STATUS
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approved
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