What That Mean "In Base 18"? i am a programmer who interest in math , lately in palindromic numbers , so if it's stupid question i am sorry ! 
i was reading about palindromic numbers in wikipedia , at some point it says 

In base 18, some powers of seven are palindromic:

 - 7^3 =     111
 - 7^4 =     777
 - 7^6 =   12321
 - 7^9 = 1367631

What that mean , In Base 18 , Thanks in advance

For example, $12321_{18}=1\cdot 18^4+2\cdot 18^3+3\cdot 18^2+2\cdot 18+1=117649_{10} \\ =1\cdot 10^5+1\cdot 10^4+7\cdot 10^3+6\cdot 10^2+4\cdot 10+9=7^6$
