

A280309


Number of n X 1 0..2 arrays with no element equal to more than one of its horizontal and vertical neighbors, with the exception of exactly two elements, and with new values introduced in order 0 sequentially upwards.


5



0, 0, 0, 1, 2, 9, 34, 124, 432, 1464, 4848, 15768, 50528, 159920, 500832, 1554304, 4785664, 14632704, 44465664, 134378112, 404089344, 1209699584, 3606669824, 10713166848, 31713660928, 93585811456, 275367776256, 808068888576
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,5


COMMENTS

Column 1 of A280313.


LINKS

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


FORMULA

Empirical: a(n) = 6*a(n1)  6*a(n2)  16*a(n3) + 12*a(n4) + 24*a(n5) + 8*a(n6) for n>10.
Empirical g.f.: x^4*(1  4*x + 3*x^2 + 8*x^3  6*x^4  12*x^5  4*x^6) / (1  2*x  2*x^2)^3.  Colin Barker, Feb 19 2018


EXAMPLE

All solutions for n=6:
..0. .0. .0. .0. .0. .0. .0. .0. .0
..0. .1. .0. .1. .0. .0. .1. .1. .0
..0. .2. .0. .1. .1. .0. .1. .0. .0
..0. .2. .0. .1. .1. .1. .1. .0. .0
..1. .2. .1. .1. .1. .1. .1. .0. .1
..0. .2. .1. .0. .1. .1. .2. .0. .2


CROSSREFS

Cf. A280313.
Sequence in context: A000524 A289614 A120989 * A010763 A077234 A091526
Adjacent sequences: A280306 A280307 A280308 * A280310 A280311 A280312


KEYWORD

nonn


AUTHOR

R. H. Hardin, Dec 31 2016


STATUS

approved



