A215121 Strobogrammatic palindromic numbers in their Roman numeral representation.

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

Offset

1,2

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).

Links

Table of n, a(n) for n=1..7.

Example

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

Crossrefs

Cf. A000787, A006968, A078715, A166874.

Sequence in context: A163467 A143045 A156909 * A329850 A175569 A275020

Adjacent sequences: A215118 A215119 A215120 * A215122 A215123 A215124

Keyword

nonn,base,fini,full

Author

Jonathan Vos Post, Aug 03 2012

Status

approved