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.