You cannot hope to achieve success without infinite perseverance. 13 can be the center of a 3x3 magic square. 13 can be the center of a 5x5 magic square. The dihedral group is the symmetry group of the square. It can act on magic squares to form new magic squares.
Dihedral groups arise frequently in art and nature.
There was a rich tradition of mental calculations among illiterate people in certain parts of Africa. Yet, the slave trade was extremely destructive to the development of mathematics. Knowledge was sometimes kept secret and only transmitted from father to son. Thus, when an expert was taken prisoner and sold as a slave, his specific professional knowledge might disappear completely from his village or region. Even though he was illiterate, with his good visualization and amazing calculation ability, Thomas Fuller was a blaring contradiction to those who tried to prove that African Americans were mentally inferior to whites.