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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Aug 10 2008
STATUS
approved