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A251122 Number of (n+1) X (2+1) 0..1 arrays with no 2 X 2 subblock having the sum of its diagonal elements greater than the maximum of its antidiagonal elements. 1
21, 40, 69, 117, 193, 315, 510, 823, 1326, 2136, 3442, 5550, 8955, 14458, 23355, 37743, 61015, 98661, 159564, 258097, 417516, 675450, 1092784, 1768032, 2860593, 4628380, 7488705, 12116793, 19605181, 31721631, 51326442, 83047675, 134373690 (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) = 4*a(n-1) - 5*a(n-2) + a(n-3) + 2*a(n-4) - a(n-5).

Empirical g.f.: x*(21 - 44*x + 14*x^2 + 20*x^3 - 12*x^4) / ((1 - x)^3*(1 - x - x^2)). - Colin Barker, Nov 25 2018

EXAMPLE

Some solutions for n=4:

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

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

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

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

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

CROSSREFS

Column 2 of A251128.

Sequence in context: A339004 A270667 A020220 * A084856 A070666 A320775

Adjacent sequences:  A251119 A251120 A251121 * A251123 A251124 A251125

KEYWORD

nonn

AUTHOR

R. H. Hardin, Nov 30 2014

STATUS

approved

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Last modified April 10 19:06 EDT 2021. Contains 342853 sequences. (Running on oeis4.)