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a(n) = (4*n+3)*(4*n+5)*(4*n+7).
2

%I #11 Jun 13 2015 00:52:31

%S 105,693,2145,4845,9177,15525,24273,35805,50505,68757,90945,117453,

%T 148665,184965,226737,274365,328233,388725,456225,531117,613785,

%U 704613,803985,912285,1029897,1157205,1294593,1442445,1601145,1771077,1952625

%N a(n) = (4*n+3)*(4*n+5)*(4*n+7).

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-6,4,-1).

%F G.f.: 3*(35 + 91*x + x^2 + x^3)/(1-x)^4.

%F E.g.f: (105 + 588*x + 432*x^2 + 64*x^3)*exp(x).

%F sum(4/a(m), m=0..infinity) = 5/6 - Pi/4.

%p seq((4*n+3)*(4*n+5)*(4*n+7),n=0..40);

%K nonn,easy

%O 0,1

%A _Miklos Kristof_, Jan 02 2008