smc

Prime factorizing this gives us $2^{15}\cdot 3^5\cdot 5^{15}=10^{15}\cdot 3^5=243\cdot 10^{15}$. $10^{15}$ has $15$ digits and $243$ = $2.43\ast 10^2$ gives us $3$ more digits. $16+2=\text{18}$ $2.43\ast 10^{17}$ has $18$ digits