
COMMENTS

Numbers which, written as Roman numerals, are the same upside down and backwards.
Upsidedowninvariant numbers are also called ambigrams. "Upside down" here means rotated by 180 degrees (i.e., central symmetry), NOT "vertically flipped" (symmetry w.r.t. horizontal line).
V, L, C, D, M (5, 50, 100, 500, 1000 in decimal) are not the same upsidedown. Excludes "old style" Roman numeral representation of n (e.g., IIII rather than IV).


EXAMPLE

I, II, III, X, XIX, XX, XXX.
