OFFSET
1,1
COMMENTS
Numbers k such that the Motzkin number A001006(k) == 0 (mod 3).
The asymptotic density of this sequence is 1 (Burns, 2016). - Amiram Eldar, Jan 30 2021
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Rob Burns, Asymptotic density of Motzkin numbers modulo small primes, arXiv:1611.04910 [math.NT], 2016.
MATHEMATICA
(* m = MotzkinNumber *) m[0] = 1; m[n_] := m[n] = m[n - 1] + Sum[m[k]*m[n - 2 - k], {k, 0, n - 2}]; Select[Range[0, 120], Mod[m[#], 3] == 0 &] (* Jean-François Alcover, Jul 10 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch and Bruce E. Sagan, Dec 05 2003
EXTENSIONS
Offset corrected by Amiram Eldar, Jan 30 2021
STATUS
approved