Number of irreducible endless self-avoiding walks of length n for the square lattice.

Terms

a(0) =4a(1) =8a(2) =24a(3) =64a(4) =200a(5) =504a(6) =1400a(7) =3648a(8) =9720a(9) =25560a(10) =67936a(11) =178464a(12) =472576a(13) =1244208a(14) =3286080a(15) =8663232a(16) =22861600a(17) =60291504a(18) =159063744a(19) =419556560a(20) =1106794584a(21) =2919596768a(22) =7701735288a(23) =20316965760a(24) =53595401400a(25) =141384847344a(26) =372973574160a(27) =983911970608