A130546 Denominators of 2*Sum_{k=1..n} 1/binomial(2*k,k), n >= 1.

1, 3, 30, 210, 315, 6930, 16380, 60060, 1021020, 19399380, 461890, 37182145, 106234700, 75482550, 166363540200, 5157269746200, 1719089915400, 12033629407800, 445244288088600, 445244288088600, 588871477794600, 784965679900201800, 1177448519850302700, 55340080432964226900

Offset

1,2

Comments

Numerators are given by A130545.

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.

Links

Table of n, a(n) for n=1..24.

Formula

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

Mathematica

Accumulate[Table[2 1/Binomial[2n, n], {n, 30}]]//Denominator (* Harvey P. Dale, Aug 12 2022 *)

Prog

(PARI) a(n) = denominator(2*sum(k=1, n, 1/binomial(2*k, k))); \\ Michel Marcus, Nov 09 2019

Crossrefs

Cf. A130545 (numerators).

Sequence in context: A003771 A121100 A203366 * A051133 A332426 A043030

Adjacent sequences: A130543 A130544 A130545 * A130547 A130548 A130549

Keyword

nonn,frac,easy

Author

Wolfdieter Lang, Jul 13 2007

Extensions

More terms from Michel Marcus, Nov 09 2019

Status

approved