Expansion of Sum_{n>=0} x^n * Sum_{k=0..n} C(n,k)^2 * x^(3*k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =5a(6) =10a(7) =17a(8) =27a(9) =46a(10) =86a(11) =165a(12) =308a(13) =558a(14) =1006a(15) =1841a(16) =3421a(17) =6383a(18) =11863a(19) =21966a(20) =40697a(21) =75662a(22) =141099a(23) =263429a(24) =491778a(25) =918104a(26) =1715259a(27) =3208078a(28) =6005818a(29) =11250198