

A183905


Number of nondecreasing arrangements of n+2 numbers in 0..2 with each number being the sum mod 3 of two others.


1



1, 4, 10, 17, 25, 34, 44, 55, 67, 80, 94, 109, 125, 142, 160, 179, 199, 220, 242, 265, 289, 314, 340, 367, 395, 424, 454, 485, 517, 550, 584, 619, 655, 692, 730, 769, 809, 850, 892, 935, 979, 1024, 1070, 1117, 1165, 1214, 1264, 1315, 1367, 1420, 1474, 1529, 1585
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OFFSET

1,2


COMMENTS

Column 2 of A183912.


LINKS

R. H. Hardin, Table of n, a(n) for n = 1..200


FORMULA

Empirical: a(n) = (1/2)*n^2 + (7/2)*n  5 for n>1.
a(n) = Triangular number(A000217)11.
Conjectures from Colin Barker, Apr 05 2018: (Start)
G.f.: x*(1 + x + x^2  2*x^3) / (1  x)^3.
a(n) = 3*a(n1)  3*a(n2) + a(n3) for n>4.
(End)


EXAMPLE

Some solutions for n=4:
..0....0....1....0....1....0....0....0....0....0....0....0....1....0....0....0
..1....0....1....1....1....1....0....0....1....0....0....0....1....0....0....0
..2....0....1....1....1....1....0....0....1....1....1....1....2....0....0....0
..2....1....1....1....2....1....1....0....2....2....1....1....2....1....0....2
..2....2....2....2....2....1....1....1....2....2....1....2....2....1....0....2
..2....2....2....2....2....2....1....1....2....2....2....2....2....2....0....2


MATHEMATICA

Abs[Table[n (n + 1)/2  11, {n, 4, 200}]] (* Vladimir Joseph Stephan Orlovsky, Jun 12 2011 *)


CROSSREFS

Cf. A000217, A183912.
Sequence in context: A310541 A246394 A310542 * A301288 A009860 A294249
Adjacent sequences: A183902 A183903 A183904 * A183906 A183907 A183908


KEYWORD

nonn,easy


AUTHOR

R. H. Hardin, Jan 07 2011


STATUS

approved



