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A145052 One-third 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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 1 14:23 EDT 2015. Contains 261270 sequences.