Expansion of ((1+x)/(1-2x))^2.

Terms

a(0) =1a(1) =6a(2) =21a(3) =60a(4) =156a(5) =384a(6) =912a(7) =2112a(8) =4800a(9) =10752a(10) =23808a(11) =52224a(12) =113664a(13) =245760a(14) =528384a(15) =1130496a(16) =2408448a(17) =5111808a(18) =10813440a(19) =22806528a(20) =47972352a(21) =100663296a(22) =210763776a(23) =440401920a(24) =918552576a(25) =1912602624a(26) =3976200192a(27) =8254390272a(28) =17112760320