Number of self-avoiding closed walks from 0 of area n in strip Z X {0,1,2}.

Terms

a(0) =1a(1) =4a(2) =10a(3) =28a(4) =64a(5) =140a(6) =304a(7) =640a(8) =1326a(9) =2716a(10) =5502a(11) =11052a(12) =22044a(13) =43700a(14) =86180a(15) =169184a(16) =330810a(17) =644564a(18) =1251954a(19) =2424860a(20) =4684696a(21) =9029756a(22) =17368408a(23) =33343520a(24) =63899686a(25) =122259372a(26) =233568998a(27) =445600236a(28) =849014964a(29) =1615709156