a(n) = 9*a(n-1) - 9*a(n-2) + a(n-3).

Terms

a(0) =1a(1) =6a(2) =45a(3) =352a(4) =2769a(5) =21798a(6) =171613a(7) =1351104a(8) =10637217a(9) =83746630a(10) =659335821a(11) =5190939936a(12) =40868183665a(13) =321754529382