<p>I think that it must exist the both ends of the exons because those parts are required to the UTR(UnTranslated Region), therefore we should calculate the number of the possible exons in only 6 exons.</p>

<p>We can also select or exclude each exon about the 6 exons -&gt; possible case is 2(select or not) x 2 x 2 x 2 x 2 x 2 = 32<br />