There is no specific episode number. American Pie is a movie series, not a TV series, so there is no specific episode number. The scene about the family's birthday is a reference to the episode of the first movie American Pie, specifically the episode in which the main character Jim's parents and grandmother are celebrating a birthday at his home while dating Nadja, the popular girl at school, unbeknownst to the main character himself. The scene has traditional elements such as cake, balloons and the singing of a birthday song, and is full of affection and warmth.