Duplicate of A008937.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =8a(5) =15a(6) =28a(7) =52a(8) =96a(9) =177a(10) =326a(11) =600a(12) =1104a(13) =2031a(14) =3736a(15) =6872a(16) =12640a(17) =23249