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A081603 Number of 2's in ternary representation of n. 47
0, 0, 1, 0, 0, 1, 1, 1, 2, 0, 0, 1, 0, 0, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 2, 2, 3, 0, 0, 1, 0, 0, 1, 1, 1, 2, 0, 0, 1, 0, 0, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 2, 2, 3, 2, 2, 3, 3, 3, 4, 0, 0, 1, 0, 0, 1, 1, 1, 2, 0, 0, 1, 0, 0, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,9
COMMENTS
Fixed point of the morphism: 0 ->001; 1 ->112; 2 ->223; 3 ->334, etc., starting from a(0)=0. - Philippe Deléham, Oct 26 2011
LINKS
F. T. Adams-Watters and F. Ruskey, Generating Functions for the Digital Sum and Other Digit Counting Sequences, JIS 12 (2009) 09.5.6.
Eric Weisstein's World of Mathematics, Ternary.
FORMULA
a(n) = floor(n/2) if n < 3, otherwise a(floor(n/3)) + floor((n mod 3)/2).
A077267(n) + A062756(n) + a(n) = A081604(n);
a(n) = (A053735(n) - A062756(n))/2.
MAPLE
A081603 := proc(n)
local a, d ;
a := 0 ;
for d in convert(n, base, 3) do
if d= 2 then
a := a+1 ;
end if;
end do:
a;
end proc: # R. J. Mathar, Jul 12 2016
MATHEMATICA
Table[Count[IntegerDigits[n, 3], 2], {n, 0, 6!}] (* Vladimir Joseph Stephan Orlovsky, Jul 25 2009 *)
Nest[ Flatten[# /. a_Integer -> {a, a, a + 1}] &, {0}, 5] (* Robert G. Wilson v, May 20 2014 *)
DigitCount[Range[0, 120], 3, 2] (* Harvey P. Dale, Jul 10 2019 *)
PROG
(Haskell)
a081603 0 = 0
a081603 n = a081603 n' + m `div` 2 where (n', m) = divMod n 3
-- Reinhard Zumkeller, Feb 21 2013
(PARI) a(n)=hammingweight(digits(n, 3)\2); \\ Ruud H.G. van Tol, Dec 10 2023
CROSSREFS
Sequence in context: A091970 A093955 A330168 * A273513 A330005 A165277
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, Mar 23 2003
STATUS
approved

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Last modified March 19 01:22 EDT 2024. Contains 370952 sequences. (Running on oeis4.)