已知数列{an}满足a1=73,an+1=3an-4n+2(n∈N*)
(1)求a2,a3的值;
(2)证明数列{an-2n}是等比数列,并求出数列{an}的通项公式;
(3)若数列{bn}满足1+2bnbn=ann(n∈N*),求数列{bn}的前n项和Sn.