repeat with i from 1 to 3999
　　set aRes to numberToRomanNumerals(i) of me
　　set bRes to romanNumeralsToNumber(aRes) of me
　　log {i, aRes, bRes}
end repeat

–Roman Number String Encoder
on numberToRomanNumerals(aNum)
　　if (aNum < 0 or aNum > 3999) then return "" –条件が間違っていたので直した（2017/5/18）
　　
　　set r_ones to {"I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"}
　　set r_tens to {"X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"}
　　set r_hunds to {"C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"}
　　set r_thouds to {"M", "MM", "MMM", "MMMM", "MMMMM", "MMMMMM", "MMMMMMM", "MMMMMMMM", "MMMMMMMMM"}
　　
　　set ones to aNum mod 10
　　set tens to (aNum – ones) mod 100
　　set hundreds to (aNum – tens – ones) mod 1000
　　set thou to (aNum – hundreds – tens – ones) mod 10000
　　
　　set tens to tens / 10
　　set hundreds to hundreds / 100
　　set thou to thou / 1000
　　
　　set rNum to current application’s NSString’s stringWithString:""
　　
　　if thou > 0 then set rNum to rNum’s stringByAppendingString:(item thou of r_thouds)
　　if hundreds > 0 then set rNum to rNum’s stringByAppendingString:(item hundreds of r_hunds)
　　if tens > 0 then set rNum to rNum’s stringByAppendingString:(item tens of r_tens)
　　if ones > 0 then set rNum to rNum’s stringByAppendingString:(item ones of r_ones)
　　
　　return rNum as text
end numberToRomanNumerals

–Roman Number String Decoder
on romanNumeralsToNumber(str)
　　— Piero Garzotto (http://scriptbuilders.net/files/romannumerals1.0.html)
　　local str, r, i
　　set r to 0
　　repeat with i from 1 to count str
　　　　set r to r + (item (offset of (item i of str) in "mdclxvi") of ¬
　　　　　　{1000, 500, 100, 50, 10, 5, 1}) * (((((offset of ¬
　　　　　　(item (i + 1) of (str & "@")) in "mdclxvi@") ≥ (offset of ¬
　　　　　　(item i of str) in "mdclxvi")) as integer) * 2) – 1)
　　end repeat
　　return r
end romanNumeralsToNumber