Third row of A113435.

Terms

a(0) =1a(1) =4a(2) =16a(3) =62a(4) =237a(5) =901a(6) =3418a(7) =12956a(8) =49096a(9) =186029a(10) =704861a(11) =2670692a(12) =10119152a(13) =38341126a(14) =145273353a(15) =550436561a(16) =2085588866a(17) =7902239404a(18) =29941371656a(19) =113447051497a(20) =429847830217