Number of zig-zag paths from top to bottom of a rectangle of width 8 with n rows.

Terms

a(0) =8a(1) =14a(2) =26a(3) =48a(4) =90a(5) =168a(6) =316a(7) =592a(8) =1114a(9) =2090a(10) =3932a(11) =7382a(12) =13884a(13) =26076a(14) =49032a(15) =92110a(16) =173170a(17) =325360a(18) =611618a(19) =1149248a(20) =2160212a(21) =4059360a(22) =7629882a(23) =14338290a(24) =26949004a(25) =50644750a(26) =95185300a(27) =178883252a(28) =336200648a(29) =631835054