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A089119
Complement of ((3*A005836) union (3*A005836 - 1) union (3*A005836 - 2)).
4
4, 5, 6, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 31, 32, 33, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 85, 86, 87, 94, 95, 96, 97, 98, 99, 100, 101, 102
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
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
Sequence in context: A310571 A280382 A055033 * A063833 A260107 A167434
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset corrected by Amiram Eldar, Jan 30 2021
STATUS
approved