已知数列{an}满足a1=33,an+1-an=2n,则
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∵数列{an}满足a1=33,an+1-an=2n,
∴当n≥2时,an=(an-an-1)+(an-1-an-2)+…+(a2-a1)+a1
=2(n-1)+2(n-2)+…+2×2+2×1+33
=2×
+33(n-1)×(n-1+1) 2
=n2-n+33,
上式对于n=1时也成立.
∴an=n2-n+33.
∴
=n+an n
-1.33 n
令f(x)=x+
-1(x>0).33 x
则f′(x)=1-
=33 x2
.x2-33 x2
由f′(x)>0,解得x>
;由f′(x)<0,解得0<x<33
.33
∴函数f(x)在[
,+∞)上单调递增;在(0,33
]上单调递减.33
∵n∈N*,∴当n=5或6时,f(n)=
取得最小值.an n
而f(6)=6+
-1=33 6
,f(5)=5+21 2
-1=33 5
>53 5
,21 2
∴则
的最小值为f(6)=an n
.21 2
故答案为
.21 2