Configurations of linear chains in a square lattice.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =32a(5) =128a(6) =344a(7) =1072a(8) =3400a(9) =9832a(10) =27600a(11) =77000a(12) =211736a(13) =572560a(14) =1534512a(15) =4072664a(16) =10725424a(17) =28035128a(18) =72831272a(19) =188139616a(20) =483452824a(21) =1236865976a(22) =3150044696a(23) =7994665480a(24) =20209319824a(25) =50942982080