OFFSET
0,3
COMMENTS
Weight of n means count of nonzero digits of n. - Daniel Forgues, Mar 24 2010
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Daniel Forgues, Table of n, a(n) for n = 0..100000
P. Flajolet and Lyle Ramshaw, A note on Gray code and odd-even merge, SIAM J. Comput. 9 (1980), 142-158.
Michael Gilleland, Some Self-Similar Integer Sequences
FORMULA
a(3n)=a(n), a(3n+1)=a(n)+1, a(9n+2)=a(n)+2, a(9n+5)=a(3n+2)+1, a(9n+8)=a(3n+2).
a(n) = Sum_{k>0} floor(|2*sin(n*Pi/3^k)|). - Toshitaka Suzuki, Sep 10 2006
MATHEMATICA
a[n_] := With[{q=Round[n/3]}, Abs[n-3q]+a[q]]; a[0]=0; Table[a[n], {n, 0, 105}](* Jean-François Alcover, Nov 25 2011, after Pari *)
PROG
(Lisp) (defun btw (n) (if (= n 0) 0 (multiple-value-bind (q r) (round n 3) (+ (abs r) (btw q)))))
(PARI) a(n)=local(q); if(n<=0, 0, q=round(n/3); abs(n-3*q)+a(q))
(Python)
def a(n):
s=0
x=0
while n>0:
x=n%3
n//=3
if x==2:
x=-1
n+=1
if x!=0: s+=1
return s
print([a(n) for n in range(101)]) # Indranil Ghosh, Jun 07 2017
CROSSREFS
KEYWORD
easy,nonn,nice
AUTHOR
EXTENSIONS
Additional terms from Allan C. Wechsler
STATUS
approved