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A209469
Number of n X 1 0..2 arrays with every element value z a city block distance of exactly z from another element value z.
1
1, 2, 5, 10, 21, 46, 97, 207, 437, 920, 1941, 4090, 8630, 18217, 38456, 81197, 171420, 361878, 763917, 1612552, 3403944, 7185413, 15167839, 32018305, 67588649, 142675574, 301179445, 635771007, 1342072303, 2833028679, 5980341655
OFFSET
1,2
COMMENTS
Column 1 of A209476.
LINKS
FORMULA
Empirical: a(n) = 3*a(n-1) - 2*a(n-2) - a(n-4) + 4*a(n-5) - 3*a(n-6) + 3*a(n-7) + a(n-8) - 2*a(n-9) + a(n-10) - a(n-11).
Empirical g.f.: x*(1 + x + x^2)*(1 - 2*x + 2*x^2 - x^3 + x^4 + x^5 - x^6 + x^7 - x^8) / (1 - 3*x + 2*x^2 + x^4 - 4*x^5 + 3*x^6 - 3*x^7 - x^8 + 2*x^9 - x^10 + x^11). - Colin Barker, Jul 10 2018
EXAMPLE
Some solutions for n=8:
..0....0....1....0....0....0....2....1....0....2....0....1....0....0....2....0
..0....2....1....1....0....0....2....1....0....2....1....1....0....0....0....1
..0....0....1....1....0....1....2....0....1....2....1....0....2....0....2....1
..1....2....1....1....0....1....2....2....1....2....2....0....2....1....0....0
..1....0....0....1....0....0....2....0....1....0....0....0....2....1....0....0
..0....1....0....0....0....1....1....2....0....1....2....0....2....2....1....0
..1....1....1....1....0....1....1....0....1....1....1....0....1....0....1....0
..1....0....1....1....0....1....0....2....1....1....1....0....1....2....0....0
CROSSREFS
Cf. A209476.
Sequence in context: A052540 A018106 A247594 * A208275 A327764 A192317
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 09 2012
STATUS
approved