A Friedman number, named after Stetson University mathematician Erich Friedman, is a number that can be calculated using its own digits, such as 736 = 36 + 7 or 3281 = (38 + 1) / 2.
A “nice” Friedman number is one in which the digits are used in order, such as 3685 = (36 + 8) × 5 or 3972 = 3 + (9 × 7)2.
Might this be done in other number systems? In a sense all Roman numerals are automatically Friedman numbers, but there are some interesting nontrivial examples as well:
XVIII = IV × II + X
LXXXIII = IXX×X/L + II
And it turns out that “nice” examples are possible here too, in which a number’s letters are used in order:
LXXVI = L / X × XV + I
LXXXIV = LX / X × XIV
Is there more? Friedman has begun looking for examples in Mayan numerals — see his website.