##Ahnentafel##
[BCG] A genealogical numbering system in which a compiler assigns number 1 to a subject, 2 to the subject's father, 3 to the subject's mother, and continues by using double each person's number for that person's father and double the person's number plus 1 for that person's mother.
[Wikipedia 2015-10-26] Also known as the Eytzinger Method, Sosa Method, and Sosa-Stradonitz Method, allows for the numbering of ancestors beginning with a descendant. This system allows one to derive an ancestor's number without compiling the list and allows one to derive an ancestor's relationship based on their number. The number of a person's father is the double of their own number, and the number of a person's mother is the double of their own, plus one. For instance, if the number of John Smith is 10, his father is 20, and his mother is 21.