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

Terms

a(0) =3a(1) =12a(2) =50a(3) =108a(4) =260a(5) =542a(6) =1126a(7) =2230a(8) =4336a(9) =8246a(10) =15458a(11) =28608a(12) =52420a(13) =95240a(14) =171814a(15) =308056a(16) =549384a(17) =975130a(18) =1723482a(19) =3034498a(20) =5324180a(21) =9311762a(22) =16238070