In each series, look for the degree and direction of change between…

In each series, look for the degree and direction of change between the numbers. In other words, do the numbers increase or decrease, and by how much Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #27467