An interpolation problem in the Denjoy–Carleman classes

Inspired by some iterative algorithms useful for proving the real analyticity (or the Gevrey regularity) of a solution of a linear partial differential equation with real-analytic coefficients, we consider the following question. Given a smooth function defined on [a,b]subset of R$[a,b]\subset {\mathbb {R}}$ and given an increasing divergent sequence dn$d_n$ of positive integers such that the derivative of order dn$d_n$ of f has a growth of the type Mdn$M_{d_n}$, when can we deduce that f is a function in the Denjoy-Carleman class CM([a,b])$C<^>M([a,b])$? We provide a positive result and show that a suitable condition on the gaps between the terms of the sequence dn$d_n$ is needed.