A068011 - OEIS

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A068011

Number of subsets of {1,2,3,...,n} that sum to 0 mod 5.

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; refs; listen; history; internal format)

	OFFSET	`0,4`
	COMMENTS	`For n>2, a(n) = 2 * A068031(n).`
	LINKS	`Sophie LeBlanc, Jan 20 2002, sci.math posting`
	FORMULA	`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`
	MAPLE	`A068011_rec := proc(n); if(0 = n) then RETURN(1); fi; if(1 = (n mod 5)) then RETURN(2A068011_rec(n-1)-2^((n-1)/5)); fi; if(2 = (n mod 5)) then RETURN(2A068011_rec(n-1)-2^((n-2)/5)); fi; RETURN(2*A068011_rec(n-1)); end;`
	CROSSREFS	`5th row of A068009.` `Sequence in context: A164169 A164166 A164161 * A048238 A048140 A179817` `Adjacent sequences: A068008 A068009 A068010 * A068012 A068013 A068014`
	KEYWORD	`nonn`
	AUTHOR	`Antti Karttunen, Feb 11 2002`

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Last modified February 15 08:06 EST 2012. Contains 205718 sequences.