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 A078715 Palindromic Roman numerals. 7
 1, 2, 3, 5, 10, 19, 20, 30, 50, 100, 190, 200, 300, 500, 1000, 1900, 2000, 3000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This sequence is consistent with the Roman numerals as expressed in the Schildberger link. 4 (usually IV now) could be included in a variant of this sequence as IIII is sometimes used (especially on clock faces). To make this or similar sequences well-defined for numbers larger than 3999, it must be decided whether and how to handle the apostrophus (backward-C), the vinculum (bar), the frame, or even other multiplier notations used at various times in representations of larger Roman numerals. Recalling the "Y2K crisis", will there be a(n even milder) "Y4M crisis"? In particular, is 4000 to be represented as MMMM, (I)(I)(I)(I) (where parentheses are used to represent C and the apostrophus), MV (with vinculum over the V), IV (with vinculum over both I and V) or IIII with vinculum over all four I's? If there is no general agreement, could Roman civilization be at risk (once again)? Indices of terms in A061493 which are also in A002113. - M. F. Hasler, Jan 12 2015 REFERENCES Encyclopaedia Britannica, 1981 ed., Vol. 11, "Mathematics, History of", p. 647. Webster's Third New International Dictionary (Unabridged), 1976 ed., "Cardinal Numbers Table" and footnotes, p. 1549. LINKS P. Lewis, ROMAN NUMERALS AND DATES Gerard Schildberger, The first 3999 numbers in Roman numerals Eric Weisstein's World of Mathematics, Roman Numeral. FORMULA A136522(A061493(a(n))) = 1. - Reinhard Zumkeller, Apr 14 2013 EXAMPLE I, II, III, V, X, XIX, XX, XXX, L, C, CXC, CC, CCC, D, M, MCM, MM, MMM PROG (Haskell) a078715 n = a078715_list !! (n-1) a078715_list = filter ((== 1) . a136522 . a061493) [1..3999] -- Reinhard Zumkeller, Apr 14 2013 (PARI) is_A078715(n)=Vecrev(n=Str(A061493(n)))==Vec(n) \\ M. F. Hasler, Jan 12 2015 CROSSREFS Cf. A061493, A006968 (Roman numerals main entry), A002113 (Palindromic Arabic numerals). Subsequence of A093703. Sequence in context: A065053 A237250 A283314 * A166874 A046630 A177874 Adjacent sequences:  A078712 A078713 A078714 * A078716 A078717 A078718 KEYWORD base,easy,nonn AUTHOR Rick L. Shepherd, Dec 19 2002 STATUS approved

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Last modified October 18 14:50 EDT 2019. Contains 328161 sequences. (Running on oeis4.)