Arrange 1 to 9 in a grid so that every row, every column, and both diagonals add to the SAME number — fifteen. The oldest, the Lo Shu, was said to appear on a turtle’s shell from the River Lo; medieval magic tied each planet to its own square. The balance is real and rare; the talisman is the belief. Slide to light up the eight equal lines.
A magic square places distinct integers so all rows, columns, and both main diagonals share a MAGIC CONSTANT. The 3×3 Lo Shu (4 9 2 / 3 5 7 / 8 1 6) uses 1–9 with constant M = n(n²+1)/2 = 15; it is essentially unique up to rotation/reflection. Renaissance magic assigned squares to the seven planets (Saturn=3×3). A fail-loud self-check throws unless all eight lines of the Lo Shu equal 15. ◆ the equal-sum structure is exact, node-verified.
LIT: the eight lines summing to 15 is exact combinatorics (and the 3×3 is unique). AMBER: the planetary/talismanic significance is the belief system built around a genuine mathematical curiosity — presented, not endorsed.