a(n) = 11*5^n-1.

Terms

a(0) =10a(1) =54a(2) =274a(3) =1374a(4) =6874a(5) =34374a(6) =171874a(7) =859374a(8) =4296874a(9) =21484374a(10) =107421874a(11) =537109374a(12) =2685546874a(13) =13427734374a(14) =67138671874a(15) =335693359374