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A229439 Number of n X 2 0..2 arrays with horizontal differences mod 3 never 1, vertical differences mod 3 never -1, and rows and columns lexicographically nondecreasing. 1
4, 7, 13, 25, 47, 84, 142, 228, 350, 517, 739, 1027, 1393, 1850, 2412, 3094, 3912, 4883, 6025, 7357, 8899, 10672, 12698, 15000, 17602, 20529, 23807, 27463, 31525, 36022, 40984, 46442, 52428, 58975, 66117, 73889, 82327, 91468, 101350, 112012, 123494 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

Empirical: a(n) = (1/24)*n^4 + (1/12)*n^3 - (1/24)*n^2 + (23/12)*n + 2.

Conjectures from Colin Barker, Sep 16 2018: (Start)

G.f.: x*(4 - 13*x + 18*x^2 - 10*x^3 + 2*x^4) / (1 - x)^5.

a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5.

(End)

EXAMPLE

Some solutions for n=4:

..0..2....0..2....0..2....1..1....0..2....0..2....0..2....0..0....0..2....0..2

..0..2....0..2....1..0....1..1....1..0....0..2....0..2....1..1....1..0....0..2

..0..2....0..2....2..1....1..1....1..0....1..0....1..0....2..2....2..1....1..0

..0..2....1..0....2..1....1..1....1..1....1..1....1..0....2..2....2..2....2..1

CROSSREFS

Column 2 of A229445.

Sequence in context: A039694 A341843 A248098 * A000288 A074863 A118334

Adjacent sequences: A229436 A229437 A229438 * A229440 A229441 A229442

KEYWORD

nonn

AUTHOR

R. H. Hardin, Sep 23 2013

STATUS

approved

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Last modified February 4 19:25 EST 2023. Contains 360059 sequences. (Running on oeis4.)