To prove:
(1) Since an+2=3an+1−2an for n∈N∗,
we have an+2−an+1=2(an+1−an) for n∈N∗.
Because a2−a1=3−1=2,
the sequence {an+1−an} is a geometric sequence with both initial term and common ratio equal to 2.
(2) From (1) we know that an+1−an=2n, and clearly, the sequence {an} is increasing, therefore
bn=an⋅an+12n−1=21⋅an⋅an+12n=21⋅an⋅an+1an+1−an=21(an1−an+11),
which leads to
Tn=21(a11−a21+a21−a31+⋯+an1−an+11)
=21(a11−an+11)
=21(1−an+11)
<21.
Hence, we conclude that Tn<21 for all n.