Numbered:

Code a (008/13) indicates that the series is numbered.  If the individual items in the series are traced as series added entries in bibliographic records, field 642 (Series Numbering Example) contains the form of series numbering to be used in the tracing.

Example:

008/13   a

130  #0  $aStructure and properties of cell membranes

642  ##  $av. 1$5DLC