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%I #12 Jun 17 2017 03:53:56
%S 1,19,118,446,1271,3017,6300,11964,21117,35167,55858,85306,126035,
%T 181013,253688,348024,468537,620331,809134,1041334,1324015,1664993,
%U 2072852,2556980,3127605,3795831,4573674,5474098,6511051,7699501
%N Principal diagonal of the convolution array A213555.
%H Clark Kimberling, <a href="/A213556/b213556.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) = (9*n^5 + 15*n^4 + 5*n^3 + n)/30.
%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 + 13*x + 19*x^2 + 3*x^3)/(1 - x)^6.
%t (See A213553.)
%Y Cf. A213553, A213500.
%K nonn,easy
%O 1,2
%A _Clark Kimberling_, Jun 17 2012
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