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Search: id:A068010
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| A068010 |
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Number of subsets of {1,2,3,...,n} that sum to 0 mod 3. |
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+0
2
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| 1, 1, 2, 4, 6, 12, 24, 44, 88, 176, 344, 688, 1376, 2736, 5472, 10944, 21856, 43712, 87424, 174784, 349568, 699136, 1398144, 2796288, 5592576, 11184896, 22369792, 44739584, 89478656, 178957312, 357914624, 715828224, 1431656448, 2863312896
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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Sophie LeBlanc, Jan 20 2002, sci.math posting
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FORMULA
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a(0)=1, a(1)=1, a(n) = 2*a(n-1) if 3 does not divide n-1 and a(n) = 2*a(n-1)-(2^((n-1)/3)) if 3 divides n-1.
a(n) = (2^n + 2^((n + 1 + (4/sqrt(3))*cos(((4*n)+1)*Pi/6))/3))/3 [Fred Galvin]
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MAPLE
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A068010 := n -> (2^n + 2^((n + 1 + (4/sqrt(3))*cos(((4*n)+1)*Pi/6))/3))/3;
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CROSSREFS
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3rd row of A068009.
Sequence in context: A050293 A048115 A047151 this_sequence A095848 A136339 A019505
Adjacent sequences: A068007 A068008 A068009 this_sequence A068011 A068012 A068013
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KEYWORD
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nonn
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AUTHOR
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Antti Karttunen, Feb 11 2002
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