A055579 - OEIS

%I #16 Sep 08 2023 13:21:08

%S 1,133,39556,16112057,7772368380,4168218286276,2403705165816240,

%T 1461462393790971585,925088518413937893358,604420266372219374357644,

%U 405139322689963395796890100,277349882927724253636179972980

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

%C This sequence satisfies a(n) = A000260(3n-1)/3. - _F. Chapoton_, Sep 08 2023

%H C. O. Oakley and R. J. Wisner, <a href="http://www.jstor.org/stable/2310544">Flexagons</a>, Amer. Math. Monthly 64 (1957), 143-154, see p. 151.

%t Table[Binomial[12n-1,3n-1]/((6n-1)(12n-1)),{n,20}] (* _Harvey P. Dale_, Nov 02 2011 *)

%o (PARI) a(n) = binomial(12*n-1,3*n-1)/((6*n-1)*(12*n-1)); \\ _Michel Marcus_, Sep 29 2017

%Y Cf. A000260.

%K nonn

%O 1,2

%A _N. J. A. Sloane_, Aug 24 2000