Number of quasi-tetrominoes in an n X n bounding box.

Terms

a(0) =0a(1) =0a(2) =1a(3) =20a(4) =147a(5) =670a(6) =2239a(7) =6138a(8) =14531a(9) =30904a(10) =60369a(11) =110300a(12) =190671a(13) =314910a(14) =500247a(15) =768810a(16) =110300a(17) =190671a(18) =314910a(19) =500247a(20) =768810a(21) =1147959a(22) =1671648