A081462 Consider the mapping f(a/b) = (a^2+b^3)/(a^3+b^2) from rationals to rationals. Starting with 1/2 (a=1, b=2) and applying the mapping to each new (reduced) rational number gives 1/2, 9/5, 103/377, ... . Sequence gives values of the denominators.

2, 5, 377, 617428, 19241552119440973526245, 6579843627298148620615676439841151690983233028443241