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 A199921 Number of Roman numerals < 4000 with n letters. 4
 7, 31, 93, 215, 389, 573, 691, 691, 573, 389, 215, 93, 31, 7, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Note that the sequence is completely symmetrical with the addition of the single (notional) Roman string of length zero. - Ian Duff, Jun 27 2017 LINKS Eric Weisstein's World of Mathematics, Roman Numerals. Wikipedia, Roman numerals EXAMPLE a(1) = 7, since there are the seven one-letter roman numerals I, V, X, L, C, D, M. a(15) = 1, since there is one fifteen-letter roman numeral MMMDCCCLXXXVIII. MAPLE for i from 1 to 15 do L[i]:={}: od: for n from 1 to 3999 do L[length(convert(n, roman))]:={op(L[length(convert(n, roman))]), n}; od: seq(nops(L[i]), i=1..15); # Martin Renner, Nov 13 2011 MATHEMATICA romanLetterCount = Table[0, {15}]; j = 1; While[j < 4000, romanLetterCount[[StringLength[IntegerString[j, "Roman"]]]]++; j++]; romanLetterCount (* Alonso del Arte, Nov 12 2011 *) PROG (Haskell) import Data.List (group, sort) a199921 n = a199921_list !! (n-1) a199921_list = map length \$ group \$ sort \$ map (a055642 . a061493) [1..3999] -- Reinhard Zumkeller, Apr 14 2013 CROSSREFS Cf. A003587, A006968. Cf. A055642, A061493. Sequence in context: A226838 A205801 A193437 * A192596 A055899 A218956 Adjacent sequences:  A199918 A199919 A199920 * A199922 A199923 A199924 KEYWORD nonn,fini AUTHOR Martin Renner, Nov 12 2011 STATUS approved

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Last modified February 25 12:01 EST 2020. Contains 332233 sequences. (Running on oeis4.)