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%I #17 Feb 11 2020 09:49:17
%S 1,2,3,10,19,20,30
%N Strobogrammatic palindromic numbers in their Roman numeral representation.
%C Numbers which, written as Roman numerals, are the same upside down and backwards.
%C 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).
%C 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).
%e I, II, III, X, XIX, XX, XXX.
%Y Cf. A000787, A006968, A078715, A166874.
%K nonn,base,fini,full
%O 1,2
%A _Jonathan Vos Post_, Aug 03 2012