

A145052


Onethird of the number of n X n nonnegative integer arrays with every 3 X 3 subblock summing to 1.


0



3, 7, 11, 15, 27, 39, 51, 87, 123, 159, 267, 375, 483, 807, 1131, 1455, 2427, 3399, 4371, 7287, 10203, 13119, 21867, 30615
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OFFSET

3,1


COMMENTS

First differences of (a(3k), a(3k + 1)), (a(3k + 1), a(3k + 2)), (a(3k + 2), a(3k + 3)) seem to be 4 * 3^(k  1).  David A. Corneth, Apr 15 2015


LINKS

Table of n, a(n) for n=3..26.


FORMULA

Conjectured g.f.: x^3*(3 + 4*x+ 4*x^2  5*x^3)/(1  x  3*x^3 + 3*x^4).  Alexander R. Povolotsky, Apr 15 2015
Conjectured formula: a(n) = 6*(3^(floor(n / 3))/3  1) + 3 + 4 * (n mod 3) * 3^(floor(n / 3))/3.  David A. Corneth, Apr 15 2015


CROSSREFS

Sequence in context: A182634 A173530 A192114 * A100900 A117829 A166092
Adjacent sequences: A145049 A145050 A145051 * A145053 A145054 A145055


KEYWORD

nonn


AUTHOR

R. H. Hardin, Sep 30 2008


STATUS

approved



