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A160676 Numbers k such that k and 2k use the same number of characters when expressed in Roman numerals. 4
2, 5, 7, 13, 18, 20, 22, 31, 36, 46, 50, 52, 55, 57, 63, 68, 70, 72, 81, 86, 95, 97, 103, 108, 123, 126, 130, 132, 135, 137, 145, 147, 153, 158, 173, 176, 180, 182, 185, 187, 198, 200, 202, 205, 207, 213, 218, 220, 222, 231, 236, 246, 254, 261, 266, 274 (list; graph; refs; listen; history; text; internal format)
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

{n: A006968(n) = A006968(2n)}. - Jonathan Vos Post, May 24 2009

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

PROG

(Haskell)

a160676 n = a160676_list !! (n-1)

a160676_list = filter (\x -> a006968 x == a006968 (2 * x)) [1..]

-- Reinhard Zumkeller, Apr 14 2013

CROSSREFS

Cf. A006968. - Jonathan Vos Post, May 24 2009

Sequence in context: A169586 A023229 A176983 * A169690 A144300 A258430

Adjacent sequences:  A160673 A160674 A160675 * A160677 A160678 A160679

KEYWORD

nonn,easy,base

AUTHOR

Claudio Meller, May 23 2009

STATUS

approved

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Last modified April 23 06:38 EDT 2021. Contains 343201 sequences. (Running on oeis4.)