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%I #12 Jul 25 2015 11:03:31
%S 1,15,81,281,756,1722,3486,6462,11187,18337,28743,43407,63518,90468,
%T 125868,171564,229653,302499,392749,503349,637560,798974,991530,
%U 1219530,1487655,1800981,2164995,2585611,3069186,3622536,4252952
%N Principal diagonal of the convolution array A213551.
%H Clark Kimberling, <a href="/A213552/b213552.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (6,-15,20,-15,6,-1).
%F a(n) = n*(1 + n)*(2 + n)(-3 + 7*n + 16*n^2)/120.
%F a(n) = 6*a(n-1) - 15*a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6).
%F G.f.: x*(1 + 9*x + 6*x^2)/(1 - x)^6.
%t (See A213551.)
%Y Cf. A213551, A213500.
%K nonn,easy
%O 1,2
%A _Clark Kimberling_, Jun 17 2012
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