Expansion of (1-x)/(1-6*x).

Terms

a(0) =1a(1) =5a(2) =30a(3) =180a(4) =1080a(5) =6480a(6) =38880a(7) =233280a(8) =1399680a(9) =8398080a(10) =50388480a(11) =302330880a(12) =1813985280a(13) =10883911680a(14) =65303470080a(15) =391820820480