Digital root number is the number mod 11 (Ɛ), for example, 1972 is 1 + 9 + 7 + 2 = 19 = 17 which is 1 + 7 = 8, while in decimal the root of the same number (3110) is 5; and in base 16 a digital root of a number is the number mod 15 (0xF), for example, 0x7DF is 7 + 13 + 15 = 35 = 0x23 which is 2 + 3 = 5, while in decimal the root of the same number (2015) is 8. Digital roots form an important mechanic in the visual novel adventure
Digital root number is a positive integer if and only if the number is itself a positive integer. The digital root of formula_1 is formula_1 itself if and only if the number has exactly one digit. The digital root of formula_1 is less than formula_1 if and only if the number is greater than or equal to 10. The digital root of formula_45 + formula_46 is digital root of the sum of the digital root of formula_45 and the digital root of formula_46. The digital root of formula_45 - formula_46 is congruent with the difference of the digital root of formula_45 and