So, in a quite understandable need for distraction, you're doodling and thinking more about what the plural of "series" should be than about the topic at hand: "serieses," "seriese," "seriesen," and "serii?"
Tako, zbog sasvim razumljive potrebe  za zabavom, škrabate i mislite više o tome kako zvuči  množina riječi "series" i o zadanoj temi: "serieses",  "seriese," "seriesen," i "serii?"