Configurations of linear chains for a square lattice.

Terms

a(0) =0a(1) =0a(2) =8a(3) =32a(4) =88a(5) =256a(6) =736a(7) =2032a(8) =5376a(9) =14224a(10) =36976a(11) =95504a(12) =243536a(13) =619168a(14) =1559168a(15) =3916960a(16) =9769072a(17) =24321552a(18) =60199464a(19) =148803824a(20) =366051864a(21) =899559584a(22) =2201636848a(23) =5384254000a(24) =13121348672a(25) =31957730688a(26) =77595810512