Central terms of triangle A249307.

Terms

a(0) =1a(1) =2a(2) =8a(3) =16a(4) =96a(5) =192a(6) =1280a(7) =2560a(8) =17920a(9) =35840a(10) =258048a(11) =516096a(12) =3784704a(13) =7569408a(14) =56229888a(15) =112459776a(16) =843448320a(17) =1686896640a(18) =12745441280a(19) =25490882560a(20) =193730707456a(21) =387461414912