Thirteen has 10 white blocks with a red border and 3 yellow blocks. His usual block arrangement are his ten block in a "ten (2x5) and three" position. However, his block arrangement change in almost every episode so it is unclear on what his actual arrangement is. He additionally has mulberry-purple eyes and eyebrows, and mouth. He also has limbs with the same colour, only with a gradient to a darker purple.He is a clumsy and unlucky Numberblock who is very prone to accidents and trouble.