Matt Parker: 145 and the Melancoil: Unhappy Numbers (アンハッピー数)

• Happification tree
• Unhappy numbers
• Melancoil numbers

Example:

145 -> 1^2 + 4^2 + 5^2 = 42 -> 4^2 + 2^2 = 20 -> 2^2 + 0^2 = 4 -> 4^2 = 16 -> 1^2 + 6^2 = 37 -> 3^2 + 7^2 = 58 -> 5^2 + 8^2 = 89 -> 8^2 + 9^2 = 145