3^(n+2)-2^(n+2)+3^n-2^n
=[3^(n+2)+3^n]-[2^(n+2)+2^n]
=[3^2*3^n+3^n]-[2^3*2^(n-1)+2*2^(n-1)]
=10*3^n-10*2^(n-1)
=10*[3^n-2^(n-1)]
能被10整除