%I A128115
%S A128115 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,
%T A128115 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,
%U A128115 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
%N A128115 Mobius inversion of A103221.
%C A128115 Number of uniform n-grammic crossed antiprisms.
%C A128115 Agrees with Mobius inversion of A008615 for n != 3. - Andrew Baxter (baxter(AT)math.rutgers.edu), 
               Jun 06 2008
%C A128115 Number of primitive equivalence classes of period 2n billiards on an 
               equilateral triangle. - Andrew Baxter (baxter(AT)math.rutgers.edu), 
               Jun 06 2008
%H A128115 Andrew M. Baxter and Ron Umble, <a href="http://arXiv.org/abs/math/0509292">
               Periodic Orbits of Billiards on an Equilateral Triangle</a>, Amer. 
               Math. Monthly, 115 (No. 6, 2008), 479-491.
%F A128115 SUM_{d|n} mu(d) * A103221(n/d), where mu is Mobius function (A008683). 
               - Andrew Baxter (baxter(AT)math.rutgers.edu), Jun 06 2008
%p A128115 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
%Y A128115 Cf. A055684.
%Y A128115 Cf. A008615, A103221.
%Y A128115 Sequence in context: A145672 A175024 A175023 this_sequence A091318 A003639 
               A061916
%Y A128115 Adjacent sequences: A128112 A128113 A128114 this_sequence A128116 A128117 
               A128118
%K A128115 nonn
%O A128115 1,11
%A A128115 Paulo de Almeida Sachs (sachs6(AT)yahoo.de), Feb 15 2007
%E A128115 Edited by Andrew Baxter (baxter(AT)math.rutgers.edu), Jun 06 2008