Benjamin Franklin built an 8x8 grid where dozens of different lines all add up the same
In 1767, Benjamin Franklin produced an 8x8 grid of the numbers 1 to 64 where every row and column sums to 260, and so do its bent diagonals and several smaller blocks within it. It's technically a 'semi-magic square' rather than a true one, since its two straight main diagonals don't share that total. Can you see how the pattern of consecutive numbers has to bend and jump across the grid to make so many different lines agree?
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Franklin built the square from interleaved arithmetic progressions rather than a simple left-to-right count, so that every row, column, bent diagonal and 2x2 block lands on 260 (or, for smaller blocks, a fixed fraction of it) without needing the two straight diagonals to cooperate. Mathematicians still study Franklin's square as an early, influential example of how much extra internal symmetry a recreational number grid can be built to contain.