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A269822 Number of n X 1 0..4 arrays with some element plus some horizontally, diagonally, antidiagonally or vertically adjacent neighbor totalling four exactly once. 2
0, 5, 40, 240, 1280, 6400, 30720, 143360, 655360, 2949120, 13107200, 57671680, 251658240, 1090519040, 4697620480, 20132659200, 85899345920, 365072220160, 1546188226560, 6528350289920, 27487790694400, 115448720916480 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 1 of A269829.

LINKS

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

FORMULA

Empirical: a(n) = 8*a(n-1) - 16*a(n-2).

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

G.f.: 5*x^2 / (1 - 4*x)^2.

a(n) = 5*4^(n-2)*(n-1).

(End)

EXAMPLE

Some solutions for n=4:

..1. .2. .2. .4. .4. .3. .2. .4. .4. .0. .0. .0. .2. .3. .3. .2

..1. .3. .3. .2. .3. .4. .2. .4. .0. .1. .0. .3. .3. .0. .1. .4

..1. .1. .2. .4. .1. .1. .3. .3. .0. .4. .4. .4. .4. .1. .0. .0

..3. .0. .2. .0. .0. .3. .3. .1. .3. .0. .1. .0. .0. .3. .3. .3

CROSSREFS

Cf. A269829.

Sequence in context: A081364 A261739 A230744 * A043019 A054604 A157794

Adjacent sequences:  A269819 A269820 A269821 * A269823 A269824 A269825

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 05 2016

STATUS

approved

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)