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A128115 Mobius inversion of A103221. 5
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; refs; listen; history; text; internal format)
OFFSET

1,11

COMMENTS

Number of uniform n-grammic crossed antiprisms.

Agrees with Mobius inversion of A008615 for n != 3. - Andrew Baxter, Jun 06 2008

Number of primitive equivalence classes of period 2n billiards on an equilateral triangle. - Andrew Baxter, Jun 06 2008

LINKS

Table of n, a(n) for n=1..98.

Andrew M. Baxter and Ron Umble, Periodic Orbits of Billiards on an Equilateral Triangle, Amer. Math. Monthly, 115 (No. 6, 2008), 479-491.

FORMULA

SUM_{d|n} mu(d) * A103221(n/d), where mu is Mobius function (A008683). - Andrew Baxter, Jun 06 2008

MAPLE

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, Jun 06 2008

CROSSREFS

Cf. A055684.

Cf. A008615, A103221.

Sequence in context: A145672 A175024 A175023 * A091318 A198898 A003639

Adjacent sequences:  A128112 A128113 A128114 * A128116 A128117 A128118

KEYWORD

nonn

AUTHOR

Paulo de Almeida Sachs (sachs6(AT)yahoo.de), Feb 15 2007

EXTENSIONS

Edited by Andrew Baxter, Jun 06 2008

STATUS

approved

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Last modified January 19 06:37 EST 2020. Contains 331033 sequences. (Running on oeis4.)