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
Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
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
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
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, Mar 23 2003
STATUS
approved