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A201976 Number of n X 3 0..3 arrays with rows and columns lexicographically nondecreasing read forwards and nonincreasing read backwards. 1
4, 72, 1372, 9260, 38112, 117744, 301612, 676792, 1375740, 2589832, 4584684, 7717252, 12454712, 19395120, 29289852, 43067824, 61861492, 87034632, 120211900, 163310172, 218571664, 288598832, 376391052, 485383080, 619485292, 783125704 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 3 of A201981.

LINKS

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

FORMULA

Empirical: a(n) = (89/36)*n^6 + (19/12)*n^5 + (215/36)*n^4 - (541/4)*n^3 + (3524/9)*n^2 - (1363/3)*n + 192.

Conjectures from Colin Barker, May 25 2018: (Start)

G.f.: 4*x*(1 + 11*x + 238*x^2 + 257*x^3 - 69*x^4 - 41*x^5 + 48*x^6) / (1 - x)^7.

a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) for n>7.

(End)

EXAMPLE

Some solutions for n=5.

..0..1..3....1..2..3....0..2..3....1..1..3....0..2..3....0..3..3....1..1..3

..2..0..3....2..2..2....1..3..2....1..1..3....1..2..1....2..0..3....1..3..2

..2..3..2....3..2..1....2..1..2....1..2..0....2..1..0....2..0..3....2..1..2

..3..1..1....3..2..1....2..2..0....2..1..0....3..0..0....3..1..2....3..3..0

..3..2..0....3..2..1....2..2..0....3..0..0....3..0..0....3..3..0....3..3..0

CROSSREFS

Cf. A201981.

Sequence in context: A060645 A203073 A231033 * A176901 A304316 A186415

Adjacent sequences:  A201973 A201974 A201975 * A201977 A201978 A201979

KEYWORD

nonn

AUTHOR

R. H. Hardin, Dec 07 2011

STATUS

approved

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Last modified June 18 20:00 EDT 2018. Contains 305571 sequences. (Running on oeis4.)