n=1,a1=6
n≥2 an=(a1×a2×a3…×a(n-1)×an)/(a1×a2×a3…a(n-1))
=(n²+3n+2)/[(n-1)²+3(n-1)+2]
=(n+1)(n+2)/(n²+n)
=(n+1)(n+2)/[n(n+1)]
=(n+2)/n
所以
an = 6 n=1
(n+2)/n n≥2