Expansion of g.f. (1+2*x)/(1-6*x).

Terms

a(0) =1a(1) =8a(2) =48a(3) =288a(4) =1728a(5) =10368a(6) =62208a(7) =373248a(8) =2239488a(9) =13436928a(10) =80621568a(11) =483729408a(12) =2902376448a(13) =17414258688a(14) =104485552128a(15) =626913312768