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a(0)=2, a(1)=5, a(n+2) = a(n+1) + (-1)^n a(n).
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%I #21 Oct 19 2017 03:14:32

%S 2,5,7,2,9,7,16,9,25,16,41,25,66,41,107,66,173,107,280,173,453,280,

%T 733,453,1186,733,1919,1186,3105,1919,5024,3105,8129,5024,13153,8129,

%U 21282,13153,34435,21282,55717,34435,90152,55717,145869,90152,236021,145869

%N a(0)=2, a(1)=5, a(n+2) = a(n+1) + (-1)^n a(n).

%C Alternate terms form a Lucas sequence.

%C Specifically, a(2n) = A022113(n). - _Jonathan Vos Post_, Nov 16 2005

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/LucasSequence.html">Lucas Sequence.</a>

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,0,1).

%F a(n) = a(n-2) + a(n-4). G.f.: (3*x^3-5*x^2-5*x-2) / (x^4+x^2-1). - _Colin Barker_, Oct 18 2013

%t CoefficientList[Series[(3*x^3 - 5*x^2 - 5*x - 2)/(x^4 + x^2 - 1), {x, 0, 50}], x] (* _Wesley Ivan Hurt_, Jan 21 2017 *)

%Y Cf. A022113.

%K nonn,easy

%O 0,1

%A _Gary W. Adamson_, Jun 06 2004

%E Edited by _Don Reble_, Nov 15 2005

%E Missing terms inserted and more terms added by _Colin Barker_, Oct 18 2013