It's the first release of the note, without the security thread. The A1 is probably the first printing run, followed by A2, A3, etc.
It's worth about 10% more than the later release with the security thread, in UNC condition.
It's a nice note, but the number isn't a premium.
As a general rule, desireable serial numbers are 1 to 1000, even thousands or millions, radar and ladder sequences, solid numbers, and a run of notes in any sequence.