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A209603 Number of n X 1 1..2 arrays with every element value z a city block distance of exactly z from another element value z. 1
0, 1, 1, 2, 2, 4, 6, 9, 13, 19, 27, 39, 57, 84, 124, 183, 269, 394, 576, 842, 1232, 1805, 2647, 3883, 5695, 8349, 12235, 17926, 26264, 38485, 56401, 82666, 121166, 177592, 260282, 381457, 559033, 819275, 1200683, 1759683, 2578965, 3779704, 5539476 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

Column 1 of A209610.

LINKS

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

FORMULA

Empirical: a(n) = 2*a(n-1) - a(n-2) + a(n-6).

Empirical g.f.: x*(1 - x + x^2 - x^3 + 2*x^4) / ((1 - x + x^3)*(1 - x - x^3)). - Colin Barker, Jul 11 2018

EXAMPLE

All solutions for n=9:

..2....2....1....1....1....2....1....1....1....2....2....1....1

..2....2....1....1....1....2....1....1....1....2....2....1....1

..2....2....2....1....1....2....1....2....1....2....2....1....2

..2....2....2....1....2....2....2....2....1....2....2....1....2

..1....2....2....1....2....2....2....2....1....2....2....2....2

..1....2....2....2....2....2....2....2....1....2....1....2....2

..1....1....2....2....2....2....2....2....1....2....1....2....1

..1....1....1....2....2....1....1....2....1....2....1....2....1

..1....1....1....2....2....1....1....2....1....2....1....2....1

CROSSREFS

Cf. A209610.

Sequence in context: A240065 A237755 A306730 * A192684 A274147 A226496

Adjacent sequences:  A209600 A209601 A209602 * A209604 A209605 A209606

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 10 2012

STATUS

approved

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Last modified January 24 13:24 EST 2020. Contains 331193 sequences. (Running on oeis4.)