An ahnentafel (German for "ancestor table"; ) or ahnenreihe ("ancestor series"; ) is a genealogical numbering system for listing a person's direct ancestors in a fixed sequence of ascent. The subject (or proband) of the ahnentafel is listed as , the subject's father as and the mother as , the paternal grandparents as and and the maternal grandparents as and , and so on, back through the generations. Apart from , who can be male or female, all even-numbered persons are male, and all odd-numbered persons are female. In this schema, the number of any person's father is double the person's number, and a person's mother is double the person's number plus one. Using this definition of numeration, one can derive some basic information about individuals who are listed without additional research.