A117905 - OEIS

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A117905

Expansion of (1+2x+2x^2)/((1-x^3)(1+x-x^3-x^4)).

1, 1, 1, 1, 3, 1, 2, 4, 2, 2, 6, 2, 3, 7, 3, 3, 9, 3, 4, 10, 4, 4, 12, 4, 5, 13, 5, 5, 15, 5, 6, 16, 6, 6, 18, 6, 7, 19, 7, 7, 21, 7, 8, 22, 8, 8, 24, 8, 9, 25, 9, 9, 27, 9, 10, 28, 10, 10, 30, 10, 11, 31, 11, 11, 33, 11, 12, 34, 12, 12, 36 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,5`
	COMMENTS	`Diagonal sums of number triangle A117904.`
	FORMULA	`a(n)=-a(n-1)+2a(n-3)+2a(n-4)-a(n-6)-a(n-7); a(n)=sum{k=0..floor(n/2), 0^abs(L(C(n-k,2)/3)-L(C(k,2)/3))} where where L(j/p) is the Legendre symbol of j and p.`
	CROSSREFS	`Sequence in context: A073892 A004608 A201673 * A133445 A139457 A049992` `Adjacent sequences: A117902 A117903 A117904 * A117906 A117907 A117908`
	KEYWORD	`easy,nonn`
	AUTHOR	`Paul Barry (pbarry(AT)wit.ie), Apr 01 2006`

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Last modified February 16 10:07 EST 2012. Contains 205904 sequences.