Whitney transform of 3^n.

Terms

a(0) =1a(1) =4a(2) =16a(3) =61a(4) =232a(5) =880a(6) =3337a(7) =12652a(8) =47968a(9) =181861a(10) =689488a(11) =2614048a(12) =9910609a(13) =37573972a(14) =142453744a(15) =540083149a(16) =2047610680a(17) =7763081488a(18) =29432076505a(19) =111585473980a(20) =423052651456