0 55660 55668 55674 55678 55684 55686 55690 55696 55698 55704 55710 55714 55716 55720 55726 55728 55734 55738 55740 55744 55746 55750 55752 55754 55755 55756 55758 55759 55760 55762 55764 55768 55770 55774 55776 55780 55786 55788 55794 55798 55800 55804 55810 55816 55818 55824 55828 55830 55836 55840 55846 55854 266669
.
，a2=
，数列｛bn｝是公差为-1的等差数列，其中bn=log2(an+1-
),｛cn｝是公比为
的等比数列，其中cn=an+1-
.试求数列｛an｝的通项公式及前n项和Sn.
}的前n项和为S′，求证：T2=(
)n. 
,求a4与S5;