Metamaterials you can count on

Mechanical metamaterials gain their material properties form their structure. Most metamaterials considered so far have a unique response that does not depend on previous driving. Here we demonstrate how internal multi-stable mechanical bits can be used to memorize previous input and respond differently as a function of an internal computation. We show a mechanical structure consisting of coupled mechanical bits that, when cyclically compressed, records the number of driving cycles: the material counts. This work lays the foundation for the study of complex memory and computation in mechanical metamaterials.