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%I #11 Jun 17 2017 02:59:44
%S 2,28,114,296,610,1092,1778,2704,3906,5420,7282,9528,12194,15316,
%T 18930,23072,27778,33084,39026,45640,52962,61028,69874,79536,90050,
%U 101452,113778,127064,141346,156660,173042
%N Principal diagonal of the convolution array A213828.
%H Clark Kimberling, <a href="/A213829/b213829.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-6,4,-1).
%F a(n) = 2*(n - 3*n^2 + 3*n^3).
%F a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4).
%F G.f.: f(x)/g(x), where f(x) = 2*x*(1 + 10*x + 7*x^2) and g(x) = (1-x)^4.
%t (See A213828.)
%Y Cf. A213828.
%K nonn,easy
%O 1,1
%A _Clark Kimberling_, Jul 04 2012