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The interactivity in the problem provides a 'hook' to engage students' curiosity, and allows them to experiment, notice patterns, make conjectures, explain what they notice and prove their conjectures. Generalisation provokes the need to use algebraic techniques such as collecting like terms and representing number sequences algebraically.
This problem follows on nicely from Number Pyramids
Can you work out what is going on in this pyramid of numbers?
(for integer values of $x$)
Students could work on Number Pyramids first in order to gain some familiarity with the structure underlying the problem.
Given the top number and either the starting number or the difference between the numbers on the bottom layer, can students work out the missing piece of information?