A238806 Number of n X 2 0..2 arrays with no element equal to one plus the sum of elements to its left or one plus the sum of the sum of elements above it, modulo 3.

3, 8, 15, 25, 39, 58, 83, 115, 155, 204, 263, 333, 415, 510, 619, 743, 883, 1040, 1215, 1409, 1623, 1858, 2115, 2395, 2699, 3028, 3383, 3765, 4175, 4614, 5083, 5583, 6115, 6680, 7279, 7913, 8583, 9290, 10035, 10819, 11643, 12508, 13415, 14365, 15359

Offset

1,1

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = (1/6)*n^3 + (23/6)*n - 1.

Conjectures from Colin Barker, Oct 24 2018: (Start)

G.f.: (3 - 4*x + x^2 + x^3) / (1 - x)^4.

a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>4.

(End)

Example

Some solutions for n=5:
..0..0....0..0....2..2....0..0....0..0....0..0....2..2....2..2....0..2....0..2
..0..0....0..0....2..1....0..0....0..2....0..2....2..1....2..1....0..2....2..1
..0..2....0..0....0..0....2..2....0..2....0..2....0..0....0..2....0..0....2..2
..0..2....0..0....0..0....2..2....2..1....0..0....0..0....0..2....0..0....0..2
..2..1....2..2....0..2....0..0....2..1....0..0....0..0....0..0....2..1....0..0

Crossrefs

Column 2 of A238812.

Sequence in context: A367064 A022451 A212772 * A080181 A071399 A001208

Adjacent sequences: A238803 A238804 A238805 * A238807 A238808 A238809

Keyword

nonn

Author

R. H. Hardin, Mar 05 2014

Status

approved