Number of n-digit palindromes.

Terms

a(0) =10a(1) =9a(2) =90a(3) =90a(4) =900a(5) =900a(6) =9000a(7) =9000a(8) =90000a(9) =90000a(10) =900000a(11) =900000a(12) =9000000a(13) =9000000a(14) =90000000a(15) =90000000a(16) =900000000a(17) =900000000a(18) =9000000000a(19) =9000000000a(20) =90000000000a(21) =90000000000a(22) =900000000000a(23) =900000000000