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A201372 Number of n X 5 0..1 arrays with rows and columns lexicographically nondecreasing read forwards, and nonincreasing read backwards. 1
2, 6, 22, 80, 268, 786, 2016, 4608, 9582, 18446, 33330, 57136, 93704, 147994, 226284, 336384, 487866, 692310, 963566, 1318032, 1774948, 2356706, 3089176, 4002048, 5129190, 6509022, 8184906, 10205552, 12625440, 15505258, 18912356, 22921216 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 5 of A201375.

LINKS

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

FORMULA

Empirical: a(n) = (1/45)*n^6 - (1/60)*n^5 - (4/9)*n^4 + (11/4)*n^3 - (206/45)*n^2 + (64/15)*n.

Conjectures from Colin Barker, May 22 2018: (Start)

G.f.: 2*x*(1 - 4*x + 11*x^2 - 9*x^3 + 15*x^4 - 6*x^5) / (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=6:

..0..1..1..1..1....0..0..0..1..1....0..0..0..1..1....0..0..0..1..1

..0..1..1..1..1....0..0..1..0..1....0..0..1..0..1....0..0..0..1..1

..0..1..1..1..1....0..1..1..1..0....0..1..0..1..0....0..1..1..0..1

..1..0..1..1..1....1..0..1..0..0....0..1..1..0..0....0..1..1..1..0

..1..1..0..0..1....1..1..0..0..0....0..1..1..0..0....1..0..1..1..0

..1..1..1..1..0....1..1..0..0..0....1..0..0..0..0....1..1..0..0..0

CROSSREFS

Cf. A201375.

Sequence in context: A150228 A203038 A206304 * A072547 A150229 A150230

Adjacent sequences:  A201369 A201370 A201371 * A201373 A201374 A201375

KEYWORD

nonn

AUTHOR

R. H. Hardin, Nov 30 2011

STATUS

approved

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Last modified December 16 06:18 EST 2019. Contains 330016 sequences. (Running on oeis4.)