Number of zig-zag paths from top to bottom of a rectangle of width 11 with n rows.

Terms

a(0) =11a(1) =20a(2) =38a(3) =72a(4) =138a(5) =264a(6) =508a(7) =976a(8) =1882a(9) =3624a(10) =6996a(11) =13488a(12) =26054a(13) =50264a(14) =97124a(15) =187440a(16) =362250a(17) =699240a(18) =1351492a(19) =2609008a(20) =5042950a(21) =9735768a(22) =18818772a(23) =36332016a(24) =70229066a(25) =135588200a(26) =262091348a(27) =506012592a(28) =978124038a(29) =1888445784