Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #10 Jan 04 2018 02:51:36
%S 3,4,5,10,17,26,37,54,83,132,211,336,535,856,1377,2222,3589,5798,9369,
%T 15146,24495,39624,64103,103708,167787,271468,439229,710674,1149881,
%U 1860530,3010381,4870878,7881227,12752076,20633275,33385320,54018559,87403840,141422361
%N a(n) = n + 2*cos((n*Pi)/3) + Lucas(n).
%C Also the number of chordless cycles in the n-prism graph for n >= 4.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ChordlessCycle.html">Chordless Cycle</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PrismGraph.html">Prism Graph</a>
%H <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (4, -6, 4, 0, -2, 1).
%F a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - 2*a(n-5) + a(n-6).
%F G.f.: x*(-3 + 8*x - 7*x^2 - 2*x^3 + 9*x^4 - 4*x^5)/((-1 + x)^2*(-1 + 2*x - x^2 + x^4)).
%t Table[n + 2 Cos[n Pi/3] + LucasL[n], {n, 20}]
%t LinearRecurrence[{4, -6, 4, 0, -2, 1}, {3, 4, 5, 10, 17, 26}, 20]
%t CoefficientList[Series[(-3 + 8 x - 7 x^2 - 2 x^3 + 9 x^4 - 4 x^5)/((-1 + x)^2 (-1 + 2 x - x^2 + x^4)), {x, 0, 20}], x]
%K nonn,easy
%O 1,1
%A _Eric W. Weisstein_, Jan 02 2018