A211094 - OEIS

%I #5 Dec 18 2015 18:18:08

%S 0,1,13,679,87781,35830153,43041488701,155818927585201,

%T 1688540173184520937,54881098051544185333873,

%U 5347007129460018897210926833

%N 1/4 the number of n X n 0..3 symmetric matrices with every element equal to one, two or three horizontal and vertical neighbors

%e Some solutions for n=4

%e ..3..3..1..0....0..0..3..3....3..3..0..0....2..2..0..0....2..2..2..0

%e ..3..3..1..0....0..3..3..2....3..3..3..3....2..2..0..1....2..2..2..0

%e ..1..1..3..3....3..3..3..2....0..3..3..1....0..0..1..1....2..2..2..0

%e ..0..0..3..3....3..2..2..2....0..3..1..1....0..1..1..1....0..0..0..0

%K nonn

%O 1,3

%A _R. H. Hardin_ Mar 31 2012