Expansion of (1-x)/(1-3*x-3*x^2-3*x^3).

Terms

a(0) =1a(1) =2a(2) =9a(3) =36a(4) =141a(5) =558a(6) =2205a(7) =8712a(8) =34425a(9) =136026a(10) =537489a(11) =2123820a(12) =8392005a(13) =33159942a(14) =131027301a(15) =517737744a(16) =2045774961a(17) =8083620018a(18) =31941398169a(19) =126212379444a(20) =498712192893