已知数列满足:a1=1,a(n+1)=an+1,n为奇数;2an,n为偶数,设bn=a2n-1,(Ⅰ)求b2,b3,并证明：b(n+1)=2bn+2;(Ⅱ)①证明：数列｛bn+2}为等比数列；②若a2k,a(2k+1),9+a(2k+2)成等比数列,求正整数k的值.

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