To convert the number given in base 7 to a bse 10 number we follow the procedure shown, that is, we need to multiply each number by the appropiate power of seven (given by their position) and then add them, then we have that:
[tex]\begin{gathered} 21603_{\text{seven}}=(2\times7^4)+(1\times7^3)+(6\times7^2)+(0\times7^1)+(3\times7^0) \\ 21603_{\text{seven}}=5442_{\text{ ten}} \end{gathered}[/tex]
Therefore:
[tex]21603_{\text{seven}}=5442_{\text{ ten}}[/tex]
