A087350 a(n) = Sum_{k=0..n} (3*n)!/(3*k)!.

1, 7, 841, 423865, 559501801, 1527439916731, 7478345832314977, 59677199741873516461, 724719913665311983902385, 12718834484826225317486856751, 309830808050366848733979830454361, 10142621332336809160155563729753961697, 434509897877308904421064350182659719099481

Offset: 0

Author

Vladeta Jovovic, Oct 20 2003

Keywords

• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..100

Crossrefs

Cf. A000522, A051396.

Programs

PARI

a(n)={sum(k=0, n, (3*n)!/(3*k)!)} \\ Andrew Howroyd, Jan 27 2020

Formula

a(n) = floor((3*n)!*C) where C = 1/3*exp(1)+2/3*exp(-1/2)*cos(1/2*3^(1/2)) = 1.16805831337591852551625692...

Extensions

Terms a(11) and beyond from Andrew Howroyd, Jan 27 2020