问题 解答题
若对于正整数k、g(k)表示k的最大奇数因数,例如g(3)=3,g(20)=5,并且g(2m)=g(m)(m∈N*),设Sn=g(1)+g(2)+g(3)+…g(2n)
(Ⅰ)求S1、S2、S3
(Ⅱ)求Sn
(III)设bn=
1
Sn-1
,求证数列{bn}的前n顶和Tn
3
2
答案

(Ⅰ)S1=g(1)+g(2)=1+1=2(1分)

S2=g(1)+g(2)+g(3)+g(4)=1+1+3+1=6(2分)

S3=g(1)+g(2)+g(3)+g(4)+g(5)+g(6)+g(7)+g(8)

=1+1+3+1+5+3+7+1=22…(3分)

(Ⅱ)∵g(2m)=g(m),n∈N+…(4分)

Sn=g(1)+g(2)+g(3)+g(4)+…+g(2n-1)+g(2n)

=[g(1)+g(3)+g(5)+…+g(2n-1)]+[g(2)+g(4)+…+g(2n)]

=[1+3+5+…+(2n-1)]+[g(2×1)+g(2×2)+…+g(2•2n-1)]…(5分)

=

(1+2n-1)•2n-1
2
+[g(1)+g(2)+…g(2n-1)]…(6分)

=4n-1+Sn-1…(7分)

Sn-Sn-1=4n-1

∴Sn=(Sn-Sn-1)+(Sn-1-Sn-2)+…+(S2-S1)+S1…(8分)

=4n-1+4n-2+…+42+4+2

=

4(4n-1-1)
4-1
+2=
1
3
4n+
2
3
…(9分)

(Ⅲ)bn=

1
Sn-1
=
3
4n-1
=
3
(2n)2-1
=
3
(2n-1)(2n+1)
=
3
2
(
1
2n-1
-
1
2n+1
),…(10分)Tn=
3
2
(
1
21-1
-
1
2+1
)+
3
2
(
1
22-1
-
1
22+1
)+
3
2
(
1
23-1
-
1
23+1
)+…+
3
2
(
1
2n-1
-
1
2n+1
)

=

3
2
[1-
1
2+1
+
1
22-1
-
1
22+1
+
1
23-1
+…+
1
2n-1-1
-
1
2n-1+1
+
1
2n-1
-
1
2n+1
]

=

3
2
[1-(
1
3
-
1
3
)-(
1
22+1
-
1
23-1
)-…-(
1
2n-1+1
-
1
2n-1
)-
1
2n+1
]…(11分)

∴当n=1时,T1=b1=1<

3
2
成立  …(12分)

当n≥2时,

1
2n-1+1
-
1
2n-1
=
2n-1-2n-1-1
(2n-1+1)(2n-1)
=
2n-1-2
(2n-1+1)(2n-1)
≥0…(13分)

Tn=

3
2
[1-(
1
2+1
-
1
22-1
)-(
1
22+1
-
1
23-1
)-…(
1
2n-1+1
-
1
2n-1
)-
1
2n+1
3
2
•1=
3
2

Tn

3
2
.…(14分)

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