f(72)=f(3^ 2乘以2^3)=f(3^2)+f(2^3)
因为f(2)=p,f(3)=q
所以f(3^2)=f(3乘以3)=2q
f(2^3)=f(2乘以2乘以2)=3p
所以f(72)=3p+2q