Percolation series for directed square lattice.

Terms

a(0) =1a(1) =0a(2) =-1a(3) =-3a(4) =-8a(5) =-21a(6) =-56a(7) =-154a(8) =-434a(9) =-1252a(10) =-3675a(11) =-10954a(12) =-33044a(13) =-100676a(14) =-309569a(15) =-957424a(16) =-2987846a(17) =-9330274a(18) =-29522921a(19) =-92459524a(20) =-298142956a(21) =-922424269a(22) =-3098690837a(23) =-9042937179a(24) =-34187149573a(25) =-79544646085