A141506 Number of n X n binary matrices, symmetric about the diagonal and under 90-degree rotation, with no more than 2 ones in any 2 X 2 subblock.

1, 2, 1, 5, 3, 25, 13, 205, 99, 2849, 1247, 66677, 26615, 2633485, 954340, 175143651, 57733315, 19638725775, 5882854746, 3710411382331, 1010373532123, 1181447019186469, 292421578705864, 633957805831439213, 142628031886778979

Offset

0,2

Links

R. H. Hardin, Table of n, a(n) for n = 0..30

Maple

solscount:= proc(vars, cons)
option remember;
   local v1, ve, c, t;
   c, t:= selectremove(type, cons, integer);
   if hastype(c, posint) then return 0 fi;
   if nops(t) = 0 then return 2^nops(vars) fi;
   v1:= vars[1];
   procname(vars[2..-1], subs(v1=0, t)) + procname(vars[2..-1], subs(v1=1, t))
end proc:
A[0]:= 1:
for n from 1 to 25 do
  M:= Matrix(n, n, shape=symmetric);
  m:= ceil(n/2);
  for i from 1 to m do
    for j from i to m do
       M[i, j]:= a[i, j];
       M[j, n+1-i]:= a[i, j];
       M[n+1-i, n+1-j]:= a[i, j];
       M[n+1-j, i]:= a[i, j];
  od od:
  cons:= {seq(seq(M[i, j]+M[i, j+1]+M[i+1, j]+M[i+1, j+1]-2, i=1..n-1), j=1..n-1)};
  vars:= {seq(seq(a[i, j], j=i..m), i=1..m)};
  A[n]:= solscount(vars, cons);
od:
seq(A[n], n=0..25); # Robert Israel, Jun 22 2015

Crossrefs

Sequence in context: A113178 A108362 A171090 * A345454 A271684 A194682

Adjacent sequences: A141503 A141504 A141505 * A141507 A141508 A141509

Keyword

nonn

Author

R. H. Hardin, Aug 10 2008

Status

approved