0,3/4,2/5,5/6,4/7,7/8,7/3 (2/3)
0,3/4,2/5,5/6,4/7,7/8,21/9(6/9)
0/(1+2),3/(2+2),2/(3+2),5/(4+2),4/(5+2),7/(6+2),21/(7+2),…….k/(n+2)
(1-1)/(1+2),(2+1)/(2+2),(3-1)/(3+2),(4+1)/(4+2),(5-1)/(5+2),(6+1)/(6+2),(7-1)/(7+2),…….[n+(-1)^n]/(n+2)
7/3是不是搞错了,而是2/3?
如果是2/3,an=[n+(-1)^n]/(n+2)