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已知正项数列{an}中,a1=1,a2=2,2an2=an+12+an-12(n...
已知正项数列{a
n}中,a
1=1,a
2=2,2a
n2=a
n+12+a
n-12(n≥2),则a
6等于( )
A.16
B.8
C.
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D.4
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