How's Your Ahnentafel ?

“Where would we be without prime numbers, Grandpa ?”
That’s the kind of question I have to cope with from my grandson, now in his last year at school studying maths and physics. I’ve even deserted my Iain Banks & Lee Child books in favour of Brian Greene, “The Hidden Reality” (well hidden indeed for a pensioner), to try and repair our communications!

In the latter book the author always chooses the difficile word (see, it’s catching), so in recent genealogy correspondence when “Ahnentafel” was mentioned I thought 'here we go again; or have I missed a village near Dumfries where I was born' ?
As it turns out, I should have known about an “Ahnentafel”, being a keen genealogist, everybody in the Society should know, so here goes, with the explanation.

An “Ahnentafel” is a German word for “ancestor table” and is a list of one’s ancestors, so constructed, that it is easy to calculate the various relationships.
The first “Ahnentafel” was published by Michael Eytzinger in 1590 - see the illustration. He was an Austrian historian and the same numbering system is sometimes called the “Sosa-Stradonitz System” named after the Spanish and German genealogists, Jerome de Sosa (1676) and Stephan Kekule von Stradonitz (1896).
In an “Ahnentafel” numbering system the base person 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.
Apart from the subject, who can be male or female, all even-numbered persons are male and all odd-numbered persons are female. Please no sexist comments!

For the first four generations, the numbers assigned a given person and their ancestors reflect the following relationships.
Decimal                                          Binary
1.    Person                                 1          
2.    Father                                  10
3.    Mother                                11
4.    Paternal grandfather        100        
5.    Paternal grandmother      101
6.    Maternal grandfather       110
7.    Maternal grandmother     111
8.    Great-grandfather             1000   father’s father’s father
9.    Great-grandmother           1001   father’s father’s mother
10.    Great-grandfather             1010   father’s mother’s father
11.    Great-grandmother           1011   father’s mother’s mother
12.    Great-grandfather             1100   mother’s father’s father
13.    Great-grandmother           1101   mother’s father’s mother
14.    Great-grandfather             1110   mother’s mother’s father
15.    Great-grandmother           1111   mother’s mother’s mother
For the binary write down the digit “1”, this represents the subject, and, writing from left to right write “0” for each father and “1” for each mother in the relation, ending with the ancestor of interest.
The result will be the binary representation of the ancestor’s “Ahnentafel” number.
As the example above, great-grandmother No.15 = 1111
To simplify your calculation of the conversion, in “Google”, type in, 15 to binary, to get the answer 1111 etc.


As they say in all the best books; for the “mathematically inclined reader” there are a number of websites where you can study the full application.
I just want to bring this “Ahnentafel” system to your attention.

This is a guest blog by Strath Stewart.