We study Basic Arithmetic, $$\textsf{BA}$$ introduced by Ruitenburg (Notre Dame J Formal Logic 39:18–46, 1998). $$\textsf{BA}$$ is an arithmetical theory based on basic logic which is weaker than intuitionistic logic. We show that the class of the provably total recursive functions of $$\textsf{BA}$$ is a proper sub-class of the primitive recursive functions. Three extensions of $$\textsf{BA}$$, called $$\textsf{BA}+\mathsf U$$, $$\mathsf {BA_{\mathrm c}}$$ and $$\textsf{EBA}$$ are investigated with relation to their provably total recursive functions. It is shown that the provably total (...) recursive functions of these three extensions of $$\textsf{BA}$$ are exactly the primitive recursive functions. Moreover, among other things, it is shown that the well-known MRDP theorem does not hold in $$\textsf{BA}$$, $$\textsf{BA}+\mathsf U$$, $$\mathsf {BA_{\mathrm c}}$$, but holds in $$\textsf{EBA}$$. (shrink)