Four
E-hèm…Integers are based upon numeric digits. Integers made their debut in "X Finds Out His Value", with One, Three, Four, Five, Six, Seven, and Eight making their "real" first appearances. In "The Number Playground Chronicle!", its spiritual successor, Two, Zero, and Nine are introduced. In "Thanks for 1,000,000 subscribers!", Ten is introduced. In "Thanks for 1,500,000 Subscribers!", Fifteen and Fourteen are introduced, along with the ability for integers to merge. In "Thanks for 2,000,000 subscribers!", Twelve and Sixteen are introduced, along with the ability for integers to divide.