mekso unary or binary operator: ordered inputs (n, b) where n and b are nonnegative integers and b > 1; output is the ultimate digital root of n in base-b.

Often denoted "dr". b defaults to whichever base in which n was expressed; output is in base-b. Thus, if we assume the cultural default of the traditional decimal system, then n will be expressed in this base and b will be defaulted to b = 2×5 and thus omitted (yielding an unary operator here). For a fixed base b and n = eval("n_{1n}") where "n_{i}" is a digit in base b for each i, if n**1 + n). This might be extended to values of n which are not nonnegative integers via various means such as the piecewise function based on modular arithmetic (although this breaks the intuition that dr(9.9) = 9, for example); it may also be extended to exotic bases. This is repeated self-application (left-composition) "su'i'e" until a fixed point (single-digit numeric string) is output.**