Given x2+x+1=0, so x=ω (primitive cube root of unity) with x3=1.
From the equation: x+x1=−1.
Since x3=1, value of xn+x−n has period 3:
n≡0(mod3): xn+x−n=2
n≡1,2(mod3): xn+x−n=−1
Fourth powers: (2)4=16, (−1)4=1.
For n=1 to 25: 8 multiples of 3 contribute 8×16=128, remaining 17 terms contribute 17×1=17.
Total =128+17=145.