Number of zig-zag paths from top to bottom of a rectangle of width 12 with n rows.

Terms

a(0) =12a(1) =22a(2) =42a(3) =80a(4) =154a(5) =296a(6) =572a(7) =1104a(8) =2138a(9) =4136a(10) =8020a(11) =15536a(12) =30148a(13) =58450a(14) =113472a(15) =220110a(16) =427410a(17) =829352a(18) =1610628a(19) =3125954a(20) =6071028a(21) =11784514a(22) =22887536a(23) =44431506a(24) =86293452a(25) =167532792a(26) =325373382a(27) =631721620a(28) =1226878704a(29) =2382108386