>>142
x^n=X ,y^n=Y と置く
x^(kn)-y^(kn)
=X^k-Y^k
=(X-Y){X^(k-1)+X^(k-2)Y+・・・+XY^(k-2)+Y^(k-1)}
=(X-Y)Σ[i=0〜k-1]X^(k-1-i)Y^i