The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #7 Jul 08 2016 17:47:56
%S 1,2,32,128,4096,16384,131072,524288,33554432,134217728,1073741824,
%T 4294967296,68719476736,274877906944,2199023255552,8796093022208,
%U 1125899906842624,4503599627370496,36028797018963968,144115188075855872,2305843009213693952
%N Denominators of coefficients of z^n/n! for the expansion of Fricke's hypergeometric function F_1(1/2,1/2;z).
%C The numerators are given in A274653, where one finds the definition of Fricke's F1(a,b;z) by a recurrence and references.
%D See A274653.
%F a(n) = denominator(r(n)), with the rationals (in lowest terms) defined by the recurrence
%F r(n) = ((2*n-1)^2/(4*n))*r(n-1) + 2*c(n)/(n*(2*n-1)), n >= 1, r(0) = 0, with c(n) = ((2*n)!)^2 / (n!^3*2^(4*n)).
%e See A274653.
%Y Cf. A274653.
%K nonn,easy,frac
%O 0,2
%A _Wolfdieter Lang_, Jul 07 2016