OFFSET
1,2
COMMENTS
Apparently a(n)/3 (mod 3) = A010060(n-1), the Thue-Morse sequence.
FORMULA
It appears that sequence gives k such that the coefficient of x^k equals 1 in Product_{j>=1} 1-x^(3^j).
MATHEMATICA
Reap[ For[n = 0, n <= 3000, n = n + 3, If[ Divisible[ Sum[ Binomial[2 k, k], {k, 1, n}], 3], Print[n]; Sow[n]]]][[2, 1]] (* Jean-François Alcover, Jul 01 2013 *)
Join[{0}, Position[Accumulate[Table[Binomial[2k, k], {k, 2600}]], _?( Divisible[ #, 3]&)]//Flatten] (* Harvey P. Dale, Mar 14 2020 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Benoit Cloitre, Apr 22 2003
STATUS
approved