Il numero romano MDCIX nel sistema decimale vale: 1609.
MDCIX in latino si scrive mille sescenti novem,
mentre in italiano milleseicentonove.
MDXC, MDXCI, MDXCII, MDXCIII, MDXCIV, MDXCV, MDXCVI, MDXCVII, MDXCVIII, MDXCIX, MDC, MDCI, MDCII, MDCIII, MDCIV, MDCV, MDCVI, MDCVII, MDCVIII, MDCX, MDCXI, MDCXII, MDCXIII, MDCXIV, MDCXV, MDCXVI, MDCXVII, MDCXVIII, MDCXIX, MDCXX, MDCXXI, MDCXXII, MDCXXIII, MDCXXIV, MDCXXV, MDCXXVI, MDCXXVII, MDCXXVIII