a(n) = (5^n + 10*(-6)^n)/11.

Terms

a(0) =1a(1) =-5a(2) =35a(3) =-185a(4) =1235a(5) =-6785a(6) =43835a(7) =-247385a(8) =1562435a(9) =-8983985a(10) =55857035a(11) =-325376585a(12) =2001087635a(13) =-11762385185a(14) =71795014235a(15) =-424666569785