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 A127189 E.g.f.: sqrt((1+4*x)/(1+2*x)). 0

%I

%S 1,1,-5,39,-423,5985,-105885,2269575,-57475215,1684565505,

%T -56176247925,2101511463975,-87163146984375,3969387329933025,

%U -196863216968342925,10560219055989978375,-609129291476291961375,37591662102746977850625,-2471292534125033454961125

%N E.g.f.: sqrt((1+4*x)/(1+2*x)).

%F D-finite with recurrence: a(n) +(6*n-7)*a(n-1) +8*(n-1)*(n-2)*a(n-2)=0. - _R. J. Mathar_, Jan 25 2020

%t With[{nn=20}, CoefficientList[Series[Sqrt[(1 + 4 x) / (1 + 2 x)], {x, 0, nn}], x] Range[0, nn]!] (* _Vincenzo Librandi_, Jan 26 2020 *)

%o (MAGMA) m:=20; R<x>:=PowerSeriesRing(Rationals(), m); b:=Coefficients(R!(Sqrt((1+4*x)/(1+2*x)))); [Factorial(n-1)*b[n]: n in [1..m]]; // _Vincenzo Librandi_, Jan 26 2020

%K sign

%O 0,3

%A _N. J. A. Sloane_, Mar 26 2007

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Last modified April 7 15:56 EDT 2020. Contains 333306 sequences. (Running on oeis4.)