Number of 0..2 arrays x(0..n-1) of n elements with zero n-1st difference.

Terms

a(0) =1a(1) =3a(2) =5a(3) =9a(4) =15a(5) =39a(6) =45a(7) =129a(8) =149a(9) =243a(10) =369a(11) =1365a(12) =2061a(13) =5901a(14) =5951a(15) =7785a(16) =10519a(17) =42519a(18) =59473a(19) =213561a(20) =157559a(21) =278835a(22) =503513a(23) =1553481a(24) =1051639a(25) =2491707a(26) =2981747a(27) =6622209a(28) =10056593a(29) =34139241