Stack polyominoes with square core.

Terms

a(0) =1a(1) =1a(2) =0a(3) =0a(4) =1a(5) =2a(6) =3a(7) =4a(8) =5a(9) =7a(10) =9a(11) =13a(12) =17a(13) =24a(14) =31a(15) =42a(16) =54a(17) =71a(18) =90a(19) =117a(20) =147a(21) =188a(22) =236a(23) =298a(24) =371a(25) =466a(26) =576a(27) =716a(28) =882a(29) =1088