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A229422 Number of n X 2 0..2 arrays with horizontal differences mod 3 never 1, vertical differences mod 3 never -1, rows lexicographically nondecreasing, and columns lexicographically nonincreasing. 2
5, 12, 27, 55, 102, 175, 282, 432, 635, 902, 1245, 1677, 2212, 2865, 3652, 4590, 5697, 6992, 8495, 10227, 12210, 14467, 17022, 19900, 23127, 26730, 30737, 35177, 40080, 45477, 51400, 57882, 64957, 72660, 81027, 90095, 99902, 110487, 121890, 134152 (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 + (5/12)*n^3 + (11/24)*n^2 + (25/12)*n + 2.

Conjectures from Colin Barker, Sep 15 2018: (Start)

G.f.: x*(5 - 13*x + 17*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..0....0..0....1..0....0..0....1..1....1..0....0..0....0..0....2..2....0..0

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

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

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

CROSSREFS

Column 2 of A229428.

Sequence in context: A176448 A078517 A170828 * A128439 A240187 A172426

Adjacent sequences:  A229419 A229420 A229421 * A229423 A229424 A229425

KEYWORD

nonn

AUTHOR

R. H. Hardin, Sep 22 2013

STATUS

approved

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Last modified September 18 04:22 EDT 2021. Contains 347508 sequences. (Running on oeis4.)