Number of 4-cycles in the Lucas cube Lambda(n).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =5a(6) =15a(7) =35a(8) =80a(9) =171a(10) =355a(11) =715a(12) =1410a(13) =2730a(14) =5208a(15) =9810a(16) =18280a(17) =33745a(18) =61785a(19) =112309a(20) =202840a(21) =364245a(22) =650705a(23) =1157015a(24) =2048532a(25) =3612900a(26) =6349200a(27) =11121300a(28) =19421150a(29) =33820061