Whats the pattern in Roman numerals?

Answer 1

Roman numerals have a numeral in multiples of 5 and 1; at 1, 5, 10, 50, 100, 500 and 1000....
1 = I
2 = II
3 = III
4 = IV (or IIII on old clocks, watches and sundials)
5 = V
6 = VI
7 = VII
8 = VIII
9 = IX
10 = X
20 = XX
30 = XXX
40 = XL
50 = L
60 = LX
70 = LXX
80 = LXXX
90 = XC
100 = C
500 = D
1000 = M
2000 = MM
3000 = MMM

After 3000 thousand are written by either placing a horizontal bar over a numeral, to indicate that the numeral should be multiplied by 1000, or by placing the numeral inside brackets, which also indicates that it should be multiplied by 1000. Examples...
4000 = [IV]
10000 = [X]
523000 = [DXXIII]
1000000 = [M]

The numbers 11 - 19 and 21 - 29 etc follow the same pattern as the numbers 1 to 9 but preceeded by X or XX etc. The same applies to numbers preceeded by 100s or 1000s. Some examples...
14 = XIV
44 = XLIV
88 = LXXXVIII
151 = CLI
423 = CDXXIII
666 = DCLXVI
1066 = MLXVI
2009 = MMIX