Excerpts from online encyclopedias:
An Ahnentafel is a list of one's ancestors with each one numbered in a sequential manner that makes it easy to calculate relationships. The Ahnentafel method is the most common method of numbering ancestors.
Ahnentafel is a German word that translates as “ancestor table” or, literally, a list of one’s ancestors. The same numbering system is sometimes called the Sosa-Stradonitz System, named after the Spanish genealogist Hieronymus/Jerome de Sosa, who first used it in 1676, and after the German genealogist Stephan Kekulé von Stradonitz [1863-1933], who popularized it in his 1896 Ahnentafel Atlas.
In an Ahnentafel numbering system, the proband is assigned the number one. The father of each person is assigned a number equal to double the child’s number. The mother of each person is assigned a number equal to double the child’s number plus one. As a result, the number of any child is one-half that of their parent, ignoring any remainder. For the first four generations, the numbers assigned a given person and their ancestors are reflected in the table below.
Translating this to a real person, here is an excerpt from the Ahnentafel of one well-known American, complete with Ahnentafel numbers:
The primary disadvantage of Ahnentafel numbers is that the size of each number when going back many generations becomes quite large. Someone with a documented line of descent from Charlemagne may be using Ahnentafel numbers in the billions.
|Ahnentafel||Binary||Relation to Self||F & M Atree||Gen||APG|
|4||100||paternal grandfather||proband's father's father||3||4|
|5||101||paternal grandmother||proband's father's mother||3||4|
|6||110||maternal grandfather||proband's mother's father||3||4|
|7||111||maternal grandmother||proband's mother's mother||3||4|
|8||1000||paternal great grandfather||proband's father's father's father||4||8|
|9||1001||paternal great grandmother||proband's father's father's mother||4||8|
|10||1010||paternal great grandfather||proband's father's mother's father||4||8|
|11||1011||paternal great grandmother||proband's father's mother's mother||4||8|
|12||1100||maternal great grandfather||proband's mother's father's father||4||8|
|13||1101||maternal great grandmother||proband's mother's father's mother||4||8|
|14||1110||maternal great grandfather||proband's mother's mother's father||4||8|
|15||1111||maternal great grandmother||proband's mother's mother's mother||4||8|