2,0,2,0……、
a1=2,an+a(n-1)=2
(an-1)+[a(n-1)-1]=0
an-1=-[a(n-1)-1]
an-1=(a1-1)(-1)^(n-1)
=(-1)^(n-1)
an=1+(-1)^(n-1);
1,0,1,0……、
a1=1,an+a(n-1)=1
(an-1/2)+[a(n-1)-1/2]=0
an-1/2=-[a(n-1)-1/2]
an-1/2=(a1-1/2)(-1)^(n-1)
=(1/2)(-1)^(n-1)
an=1/2+(1/2)(-1)^(n-1);