Which of the following is NOT one of the three math sequences used for understanding math?

In the context of understanding mathematical concepts, the three recognized sequences are concrete, semi-concrete, and abstract. These sequences represent a progression in learning where students begin with tangible, physical representations of mathematical ideas (concrete), move to visual or semi-concrete representations (such as drawings or models), and finally develop an understanding of abstract concepts (like symbols and numbers without physical representation).

The term "digital" does not fit into this framework as it refers more to the usage of technology or digital tools in learning rather than a method of comprehending mathematical concepts. The other sequences—concrete, abstract, and semi-concrete—are essential in helping students build a comprehensive understanding of math, as they create a pathway from hands-on experiences to abstract reasoning.