A105186 Replace odd-positioned digits with 0 in ternary representation of n.

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

Author

Reinhard Zumkeller, Apr 11 2005

Keywords

• nonn
• base

Examples

			n = 123 = '11120' --> '10100' = 90 = a(123).
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A007089, A063694, A163325.

Programs

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

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