(1+3)(1+3^2)(1+3^4)……(1+3^64)+1
=1/2*2*(1+3)(1+3^2)(1+3^4)……(1+3^64)+1
=1/2*(3-1)*(1+3)(1+3^2)(1+3^4)……(1+3^64)+1
=1/2*(3^2-1)(1+3^2)(1+3^4)……(1+3^64)+1
=1/2*(3^4-1)(1+3^4)……(1+3^64)+1
=1/2*(3^8-1)……(1+3^64)+1
.
=1/2*(3^64-1)(1+3^64)+1
=1/2*(3^128-1)+1
=1/2*3^128-1/2+1
=1/2*3^128+1/2
=1/2*(3^128+1)