The lowest
order of the
squared squares with 21 internal squares is called the
pluperfect square. It was discovered in 1978 by a
computer scientist and
mathemetician named
A.J.W. Duijvestijn.
The Bouwkamp code for the pluperfect square is {50, 35, 27}, {8, 19}, {15, 17, 11}, {6, 24}, {29, 25, 9, 2}, {7, 18}, {16}, {42}, {4, 37}, {33}.