First differences of A139784.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =1a(5) =2a(6) =4a(7) =11a(8) =19a(9) =38a(10) =76a(11) =163a(12) =315a(13) =630a(14) =1260a(15) =2563a(16) =5083a(17) =10166a(18) =20332