A055579 a(n) = binomial(12*n-1,3*n-1)/((6*n-1)*(12*n-1)).

1, 133, 39556, 16112057, 7772368380, 4168218286276, 2403705165816240, 1461462393790971585, 925088518413937893358, 604420266372219374357644, 405139322689963395796890100, 277349882927724253636179972980, 193255236433935311905233253319800, 136699584892335006608714415670858032

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..344

C. O. Oakley and R. J. Wisner, Flexagons, Amer. Math. Monthly 64 (1957), 143-154, see p. 151.

Formula

a(n) = A000260(3*n-1)/3. - F. Chapoton, Sep 08 2023

a(n) ~ 2^(24*n-9/2) / (3^(9*n+3) * n^(5/2) * sqrt(Pi)). - Amiram Eldar, Sep 18 2025

Mathematica

Table[Binomial[12n-1, 3n-1]/((6n-1)(12n-1)), {n, 20}] (* Harvey P. Dale, Nov 02 2011 *)

Prog

(PARI) a(n) = binomial(12*n-1, 3*n-1)/((6*n-1)*(12*n-1)); \\ Michel Marcus, Sep 29 2017

Crossrefs

Cf. A000260.

Sequence in context: A129049 A281496 A015264 * A191715 A208626 A061491

Adjacent sequences: A055576 A055577 A055578 * A055580 A055581 A055582

Keyword

nonn,easy

Author

N. J. A. Sloane, Aug 24 2000

Extensions

More terms from Amiram Eldar, Sep 18 2025

Status

approved