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Search: id:A068011
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| A068011 |
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Number of subsets of {1,2,3,...,n} that sum to 0 mod 5. |
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+0
2
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| 1, 1, 1, 2, 4, 8, 14, 26, 52, 104, 208, 412, 820, 1640, 3280, 6560, 13112, 26216, 52432, 104864, 209728, 419440, 838864, 1677728, 3355456, 6710912, 13421792, 26843552, 53687104, 107374208, 214748416, 429496768, 858993472, 1717986944
(list; graph; listen)
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OFFSET
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0,4
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COMMENT
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For n>2, a(n) = 2 * A068031(n).
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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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s(k+1) = 2s(k) if k == 2, 3, or 4 mod 5, 2s(k)-2^(k/5) if k == 0 mod 5, 2s(k)-2^((k-1)/5) if k == 1 mod 5
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MAPLE
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A068011_rec := proc(n); if(0 = n) then RETURN(1); fi; if(1 = (n mod 5)) then RETURN(2*A068011_rec(n-1)-2^((n-1)/5)); fi; if(2 = (n mod 5)) then RETURN(2*A068011_rec(n-1)-2^((n-2)/5)); fi; RETURN(2*A068011_rec(n-1)); end;
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CROSSREFS
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5th row of A068009.
Sequence in context: A054193 A117633 A135491 this_sequence A048238 A048140 A065616
Adjacent sequences: A068008 A068009 A068010 this_sequence A068012 A068013 A068014
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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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