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a(n) = 2^n*(n - 3) + 4.
0

%I #9 Sep 01 2017 14:10:39

%S 0,0,4,20,68,196,516,1284,3076,7172,16388,36868,81924,180228,393220,

%T 851972,1835012,3932164,8388612,17825796,37748740,79691780,167772164,

%U 352321540,738197508,1543503876,3221225476,6710886404,13958643716,28991029252,60129542148

%N a(n) = 2^n*(n - 3) + 4.

%C Also the skewness of the (n+1)-hypercube graph.

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

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

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (5, -8, 4).

%F G.f.: 4*x^3/((1 - 2*x)^2*(1 - x)).

%F a(n) = 5*a(n-1) - 8*a(n-2) + 4*a(n-3).

%F a(n) = 4*A000337(n-2), with A000337(-1) = 0.

%t Table[2^n (n - 3) + 4, {n, 20}]

%t LinearRecurrence[{5, -8, 4}, {0, 0, 4}, 20]

%t CoefficientList[Series[4 x^3/((1 - 2 x)^2 (1 - x)), {x, 0, 20}], x]

%Y Cf. A000337.

%K nonn,easy

%O 1,3

%A _Eric W. Weisstein_, Aug 25 2017