A215121 Strobogrammatic palindromic numbers in their Roman numeral representation.

1, 2, 3, 10, 19, 20, 30

Offset: 1

Author

Jonathan Vos Post, Aug 03 2012

Keywords

• nonn
• base
• fini
• full

Comments

Numbers which, written as Roman numerals, are the same upside down and backwards.

Upside-down-invariant 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 upside-down. Excludes "old style" Roman numeral representation of n (e.g., IIII rather than IV).

Examples

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

Crossrefs

Cf. A000787, A006968, A078715, A166874.