“…For example, the first of them are Now, we can construct rational function in order to have the correct limit at infinity according to the boundary conditions ; one would expect that N ≥ S . However, in order to obtain an accurate value of f 2 , it is more convenient to choose S = N + d , d = 0,1,2, … (for more details, see , so from , each Hankel determinant is a polynomial function of f 2 , and we expect that there is a sequence of roots , D = 2,3, … that converges toward the actual value of f ″ (0). In our case, because f 4 is the first nonzero coefficient that depends on f 2 , we use the Hankel sequences with d ≥ 3 to compute f ″ (0).…”