We propose that the unique ability of humans to have separate mental representations for each finger and to move them in different sequential orders were redeployed for arithmetic. We tested our hypothesis with a behavioral dual-task experiment, where subjects (N=46) solved addition problems (primary task) and performed a sentence comprehension task (control task), while concurrently tapping their fingers (secondary task). We examined two sequential finger tapping tasks: one that was more automatic and followed the anatomical finger order (simple) and one that relied heavily on sequence processing (complex). The results revealed that both simple and complex finger tapping differentially interfered with addition compared to sentence comprehension. These results provide support for a finger-based representation of numbers and shared use of sequence processing resources for finger movements and addition.