OFFSET
1,1
COMMENTS
Example: 2 and its double 4 both need two characters in Roman numerals: 2=II, 4=IV. Also 5=V, 10=X; 7=VII, 14=XIV.
LINKS
Nathaniel Johnston, Table of n, a(n) for n = 1..503 (complete up to 3999)
Eric Weisstein's World of Mathematics, Roman Numerals
Wikipedia, Roman numerals
FORMULA
MAPLE
for n from 1 to 3999 do if(length(convert(n, roman)) = length(convert(2*n, roman)))then printf("%d, ", n): fi: od: # Nathaniel Johnston, May 18 2011
MATHEMATICA
Select[Range[300], StringLength[RomanNumeral[#]]==StringLength[ RomanNumeral[ 2 #]]&] (* Harvey P. Dale, Apr 29 2022 *)
PROG
(Haskell)
a160676 n = a160676_list !! (n-1)
a160676_list = filter (\x -> a006968 x == a006968 (2 * x)) [1..]
-- Reinhard Zumkeller, Apr 14 2013
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Claudio Meller, May 23 2009
STATUS
approved