LAN party numbers.

Terms

a(0) =0a(1) =4a(2) =6a(3) =18a(4) =48a(5) =118a(6) =314a(7) =806a(8) =2082a(9) =5402a(10) =13946a(11) =36102a(12) =93378a(13) =241518a(14) =624810a(15) =1616142a(16) =4180594a(17) =10814158a(18) =27973298a(19) =72359966a(20) =187176434a(21) =484177358a(22) =1252442706a(23) =3239746862a(24) =8380393330a(25) =21677923822a(26) =56075218194a(27) =145052181998a(28) =375212720786a(29) =970578896942