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If computers or tablets are available, students could work in pairs to explore the first number pyramid. Alternatively, the concept of a number pyramid could be introduced by drawing a couple of examples on the board, and silently filling in each cell, pausing to let students reflect on what they think is happening at each stage.
"What do you think the rule is, to generate each layer of the pyramid from the layer below?"
Give students time to work on the questions that have been raised. Encourage them to experiment before trying to draw more general conclusions. As students are working, make it clear that they are expected to be able to explain and justify any generalisations they make.
If students notice patterns but can't explain them, it may be helpful to introduce algebraic representation.
Similar questions can be asked about larger pyramids. Here is an interactive four-layer number pyramid.