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Search: id:A128115
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| 0, 1, 0, 0, 1, 0, 1, 1, 1, 0, 2, 1, 2, 1, 1, 1, 3, 1, 3, 2, 2, 1, 4, 1, 3, 2, 3, 2, 5, 2, 5, 3, 3, 2, 4, 2, 6, 3, 4, 2, 7, 2, 7, 4, 4, 3, 8, 3, 7, 4, 5, 4, 9, 3, 6, 4, 6, 4, 10, 2, 10, 5, 6, 5, 8, 4, 11, 6, 7, 4, 12, 4, 12, 6, 7, 6, 10, 4, 13, 6, 9, 6, 14, 4, 10, 7, 9, 6, 15, 4, 12, 8, 10, 7, 12, 5, 16, 7
(list; graph; listen)
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OFFSET
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1,11
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COMMENT
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Number of uniform n-grammic crossed antiprisms.
Agrees with Mobius inversion of A008615 for n != 3. - Andrew Baxter (baxter(AT)math.rutgers.edu), Jun 06 2008
Number of primitive equivalence classes of period 2n billiards on an equilateral triangle. - Andrew Baxter (baxter(AT)math.rutgers.edu), Jun 06 2008
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LINKS
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Andrew M. Baxter and Ron Umble, Periodic Orbits of Billiards on an Equilateral Triangle, Amer. Math. Monthly, 115 (No. 6, 2008), 479-491.
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FORMULA
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SUM_{d|n} mu(d) * A103221(n/d), where mu is Mobius function (A008683). - Andrew Baxter (baxter(AT)math.rutgers.edu), Jun 06 2008
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MAPLE
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with(numtheory): A103221:=n->floor((n+2)/2)-floor((n+2)/3): A128115:=n->add(mobius(d)*A103221(n/d), d in divisors(n)): - Andrew Baxter (baxter(AT)math.rutgers.edu), Jun 06 2008
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CROSSREFS
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Cf. A055684.
Cf. A008615, A103221.
Sequence in context: A145672 A175024 A175023 this_sequence A091318 A003639 A061916
Adjacent sequences: A128112 A128113 A128114 this_sequence A128116 A128117 A128118
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KEYWORD
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nonn
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AUTHOR
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Paulo de Almeida Sachs (sachs6(AT)yahoo.de), Feb 15 2007
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EXTENSIONS
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Edited by Andrew Baxter (baxter(AT)math.rutgers.edu), Jun 06 2008
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