You'd have to include a small javascript in your template, which would provide the sequence number.

<script language="javascript">
<!--
// Initialize seqence number
var seqNum = 0;

function incrementSeqNumber()
{
seqNum = seqNum + 1;
}
//-->
</script>

In the section of the template where you loop thru the albums in your collection, you would have to call the incrementSeqNumber() function, and then write the resulting sequence number to your output file:

<script language="javascript">
<!--
incrementSeqNumber();
document.write(seqNum);
//-->
</script>