1)S 1= 1,S2=3,S3=4,S4=7,S5= 1 1,S6= 18。 In fact, according to the second question, you can also get a solution.
2) Direct proof is enough.
a^(n+2)+b^(n+2)=(a+b)[a^(n+ 1)+b^(n+ 1)]-ab(a^n+b^n)
That is, S[n+2]=S[n+ 1]+S[n]
3) In fact, A and B are (1+√5)/2 and (1-√5)/2, which can be verified by Vieta's theorem.
The equation to be solved is S2=3.