A130546 - OEIS

%I #9 Aug 12 2022 19:54:49

%S 1,3,30,210,315,6930,16380,60060,1021020,19399380,461890,37182145,

%T 106234700,75482550,166363540200,5157269746200,1719089915400,

%U 12033629407800,445244288088600,445244288088600,588871477794600,784965679900201800,1177448519850302700,55340080432964226900

%N Denominators of 2*Sum_{k=1..n} 1/binomial(2*k,k), n >= 1.

%C Numerators are given by A130545.

%C For the rationals r(n) := 2*Sum_{k=1..n} 1/binomial(2*k,k), n >= 1, the Comtet reference and a W. Lang link see A130545.

%F a(n) = denominator(r(n)), n >= 1.

%t Accumulate[Table[2 1/Binomial[2n,n],{n,30}]]//Denominator (* _Harvey P. Dale_, Aug 12 2022 *)

%o (PARI) a(n) = denominator(2*sum(k=1, n, 1/binomial(2*k,k))); \\ _Michel Marcus_, Nov 09 2019

%Y Cf. A130545 (numerators).

%K nonn,frac,easy

%O 1,2

%A _Wolfdieter Lang_, Jul 13 2007

%E More terms from _Michel Marcus_, Nov 09 2019