∵a 1=
1
3 . a n = a n-1 •
2n-3
2n+1
∴a 2=
1
3 .
1
5
a 3=
1
3 .
1
5 •
3
7 =
1
5 •
1
7
…
a n=
1
3 .
1
5 •
3
7 •…•
2n-5
2n-1 •
2n-3
2n+1 =
1
(2n-1)(2n+1)
当a n=
1
2303 时,(2n-1)(2n+1)=2303
又由自然数n(n≥2)
可得n=24
故选B
∵a 1=
1
3 . a n = a n-1 •
2n-3
2n+1
∴a 2=
1
3 .
1
5
a 3=
1
3 .
1
5 •
3
7 =
1
5 •
1
7
…
a n=
1
3 .
1
5 •
3
7 •…•
2n-5
2n-1 •
2n-3
2n+1 =
1
(2n-1)(2n+1)
当a n=
1
2303 时,(2n-1)(2n+1)=2303
又由自然数n(n≥2)
可得n=24
故选B