Percolation series for directed square lattice.

Terms

a(0) =1a(1) =0a(2) =-1a(3) =-2a(4) =-4a(5) =-8a(6) =-17a(7) =-38a(8) =-88a(9) =-210a(10) =-511a(11) =-1264a(12) =-3165a(13) =-8006a(14) =-20426a(15) =-52472a(16) =-135682a(17) =-352562a(18) =-920924a(19) =-2414272a(20) =-6356565a(21) =-16782444a(22) =-44470757a(23) =-118090648a(24) =-314580062a(25) =-839379548a(26) =-2245969278a(27) =-6017177104a(28) =-16161597987