The sequence of all positive plaindromes are written in ascending order $1,2,3,4,5,6,7,8,9,11,22,\mathrm{.....}$ Then

1 digit palindromes $\to 9$ 
2 digit palindromes $\to 9\times 1$
3 digit palindromes $\to 9\times 10$ 
4 digit palindromes $\to 9\times 10$ 
5 digit palindromes $\to 9\times {10}^2$ 
6 digit palindromes $\to 9\times {10}^2$ 
$1\underset{\_}{0}\underset{\_}{0}------\to 10$ 
$101------\to 10$ 
$\therefore$ Number at $2(9+90+900+10)=2018,$ rank is 1019101
$1----------\to {10}^3$ 
$20----------\to {10}^2$ 
$210----------\to 10$ 
$211\to 10$ 
$212\to 10$ 
$213\to 10$ 
$2140412\to 10$ 
Rank of 2140412 = $2(9+90+900)+1000+100+40+1$ 
$=1998+1000+100+40+1=3139$