Revert transform of (1 - x - 2x^2 + x^3)/(1 - 2x^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =20a(5) =72a(6) =272a(7) =1063a(8) =4262a(9) =17432a(10) =72448a(11) =305074a(12) =1298812a(13) =5581188a(14) =24175560a(15) =105448157a(16) =462745106a(17) =2041634108a(18) =9050879192a(19) =40296196096a(20) =180099939464a(21) =807757872276