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A105186
Replace odd-positioned digits with 0 in ternary representation of n.
1
0, 1, 2, 0, 1, 2, 0, 1, 2, 9, 10, 11, 9, 10, 11, 9, 10, 11, 18, 19, 20, 18, 19, 20, 18, 19, 20, 0, 1, 2, 0, 1, 2, 0, 1, 2, 9, 10, 11, 9, 10, 11, 9, 10, 11, 18, 19, 20, 18, 19, 20, 18, 19, 20, 0, 1, 2, 0, 1, 2, 0, 1, 2, 9, 10, 11, 9, 10, 11, 9, 10, 11, 18, 19, 20, 18, 19, 20, 18, 19, 20, 81, 82
OFFSET
0,3
LINKS
FORMULA
a(n) = n - a(floor(n/3))*3, a(0) = 0.
a(n) = 9*a(floor(n/9)) + (n mod 9) mod 3. - Reinhard Zumkeller, Sep 26 2015
EXAMPLE
n = 123 = '11120' --> '10100' = 90 = a(123).
PROG
(Haskell)
a105186 0 = 0
a105186 n = 9 * a105186 n' + mod t 3
where (n', t) = divMod n 9
-- Reinhard Zumkeller, Sep 26 2015
(PARI) a(n) = fromdigits(digits(n, 9)%3, 9); \\ Kevin Ryde, May 20 2020
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, Apr 11 2005
STATUS
approved