Palíndromos o Capicuas

a(n)= número de capicuas menores que 10^n

a(n)=2(10^(n/2) -1) si n es par
a(n)=11(10^(n-1)/2) -2 si n es impar


Number of nonzero palindromes less than 10^n.
9, 18, 108, 198, 1098, 1998, 10998, 19998, 109998, 199998, 1099998, 1999998, 10999998, 19999998, 109999998, 199999998, 1099999998, 1999999998, 10999999998, 19999999998, 109999999998, 199999999998, 1099999999998

León-Sotelo