Padovan's spiral numbers.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =3a(6) =4a(7) =5a(8) =7a(9) =9a(10) =12a(11) =16a(12) =21a(13) =28a(14) =37a(15) =49a(16) =65a(17) =86a(18) =114a(19) =151a(20) =200a(21) =265a(22) =351a(23) =465a(24) =616a(25) =816a(26) =1081a(27) =1432a(28) =1897a(29) =2513