Number of (n+1) X (n+1) 0..1 matrices with each 2 X 2 subblock idempotent.

Terms

a(0) =8a(1) =32a(2) =78a(3) =196a(4) =428a(5) =916a(6) =1858a(7) =3678a(8) =7096a(9) =13458a(10) =25150a(11) =46466a(12) =85028a(13) =154356a(14) =278298a(15) =498792a(16) =889320a(17) =1578248a(18) =2789166a(19) =4910498a(20) =8615348a(21) =15067462a(22) =26274538a(23) =45693286