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

Terms

a(0) =4a(1) =12a(2) =28a(3) =76a(4) =204a(5) =540a(6) =1404a(7) =3724a(8) =9748a(9) =25772a(10) =67940a(11) =179068a(12) =472580a(13) =1245620a(14) =3286308a(15) =8666956a(16) =22861604a(17) =60301764a(18) =159063748a(19) =419582396a(20) =1106796012a(21) =2919664716a(22) =7701735292a(23) =20317148476a(24) =53595401604a(25) =141385319932a(26) =372973583908a(27) =983913216292