%I #7 Nov 10 2014 17:35:47

%S 4,16,72,142,332,668,1356,2634,5046,9480,17594,32286,58730,106028,

%T 190204,339322,602416,1064888,1875104,3290166,5754586,10035236,

%U 17452462,30275242,52395822

%N Number of n X n 0..3 matrices with each 2 X 2 subblock idempotent.

%C Column 3 of A224665.

%F Empirical: a(n) = 6*a(n-1) -12*a(n-2) +5*a(n-3) +12*a(n-4) -12*a(n-5) -3*a(n-6) +6*a(n-7) -a(n-9) for n>10.

%e Some solutions for n=3:

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

%e ..0..0..1....1..0..0....0..0..0....0..0..0....0..0..0....1..0..1....0..0..0

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

%K nonn,more

%O 1,1

%A _R. H. Hardin_, Apr 14 2013