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

Terms

a(0) =1a(1) =4a(2) =16a(3) =60a(4) =228a(5) =864a(6) =3276a(7) =12420a(8) =47088a(9) =178524a(10) =676836a(11) =2566080a(12) =9728748a(13) =36884484a(14) =139839696a(15) =530172540a(16) =2010036708a(17) =7620627744a(18) =28891993356a(19) =109537863300a(20) =415289569968