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 A099581 Sum C(n-k,k-1)3^(n-k-1), k=0..floor(n/2). 1
 0, 0, 1, 3, 15, 54, 216, 810, 3105, 11745, 44631, 169128, 641520, 2431944, 9221121, 34959195, 132543135, 502506990, 1905156936, 7222991778, 27384465825, 103822372809, 393620574951, 1492328843280, 5657848431840, 21450531825360 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS In general a(n)=sum{k=0..floor(n/2), C(n-k,k-1)r^(n-k-1) has g.f. x^2/((1-r*x^2)(1-r*x-r*x^2)) and satisfies a(n)=r*a(n-1)+2r*a(n-2)-r^2*a(n-3)-r^2*a(n-4). LINKS Index entries for linear recurrences with constant coefficients, signature (3,6,-9,-9). FORMULA G.f.: x^2/((1-3x^2)(1-3x-3x^2)); a(n)=3a(n-1)+6a(n-2)-9a(n-3)-9a(n-4). CROSSREFS Cf. A099177, A099582. Sequence in context: A261565 A085480 A265974 * A026696 A082708 A093925 Adjacent sequences:  A099578 A099579 A099580 * A099582 A099583 A099584 KEYWORD easy,nonn AUTHOR Paul Barry, Oct 23 2004 STATUS approved

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Last modified January 21 04:53 EST 2020. Contains 331104 sequences. (Running on oeis4.)