Number of certain stackings of n+1 squares on a double staircase.

Terms

a(0) =1a(1) =1a(2) =3a(3) =6a(4) =12a(5) =23a(6) =43a(7) =79a(8) =143a(9) =256a(10) =454a(11) =799a(12) =1397a(13) =2429a(14) =4203a(15) =7242a(16) =12432a(17) =21271a(18) =36287a(19) =61739a(20) =104791a(21) =177476a(22) =299978a(23) =506111a(24) =852457a(25) =1433593a(26) =2407443a(27) =4037454a(28) =6762708a(29) =11314391