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A239980
Number of n X 2 0..3 arrays with no element equal to zero plus the sum of elements to its left or two plus the sum of elements above it or one plus the sum of the elements diagonally to its northwest, modulo 4.
1
1, 3, 6, 16, 40, 84, 208, 474, 1047, 2530, 5668, 12907, 30446, 68427, 157875, 366480, 830089, 1920870, 4421253, 10083067, 23303103, 53453752, 122448587, 282350403, 647215090, 1486007814, 3420002865, 7842656682, 18022838258, 41428828907
OFFSET
1,2
LINKS
FORMULA
Empirical: a(n) = 2*a(n-2) + 10*a(n-3) - a(n-4) - 5*a(n-5) - 15*a(n-6) + a(n-7) + 4*a(n-8) + 2*a(n-9) + 10*a(n-10) + 5*a(n-11) - 6*a(n-13).
Empirical g.f.: x*(1 + 3*x + 4*x^2 - x^4 + 4*x^6 - 4*x^7 - 6*x^8 + 6*x^9 + 6*x^10 - 4*x^12) / (1 - 2*x^2 - 10*x^3 + x^4 + 5*x^5 + 15*x^6 - x^7 - 4*x^8 - 2*x^9 - 10*x^10 - 5*x^11 + 6*x^13). - Colin Barker, Oct 26 2018
EXAMPLE
Some solutions for n=4:
..3..0....3..0....3..0....3..0....3..0....3..0....3..0....3..0....3..0....3..0
..2..1....2..1....2..1....2..3....2..1....3..1....3..1....3..1....2..1....2..1
..2..1....2..0....2..0....2..0....2..1....2..1....3..2....3..1....2..1....2..0
..3..2....3..1....3..0....3..2....3..1....3..1....2..3....2..1....2..1....3..2
CROSSREFS
Column 2 of A239986.
Sequence in context: A168317 A188442 A046211 * A205770 A301959 A018022
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 30 2014
STATUS
approved