Percolation series for directed square lattice.

Terms

a(0) =1a(1) =0a(2) =-1a(3) =-2a(4) =-2a(5) =0a(6) =2a(7) =4a(8) =3a(9) =0a(10) =-1a(11) =6a(12) =28a(13) =72a(14) =139a(15) =242a(16) =407a(17) =722a(18) =1215a(19) =2348a(20) =3753a(21) =7186a(22) =9558a(23) =21800a(24) =16576a(25) =61234a(26) =-7978a(27) =226136a(28) =-446034a(29) =1118180