Converting Ahnentafel Numbers to Relationships

An Ahnentafel (German for “ancestor table”) is a list of the ancestors of an individual. The first time you see one, you will probably find in more than a little confusing. Once you understand the strict numbering system that is the basis of the list, you will find it to be a logical representation of each ancestor generation. Ahnentafels pack lot of information in a compact format. Since no chart or graphics are needed, an Ahnentafel can be sent as plain text. That makes it useful when formatting is not possible or might be displayed incorrectly – like in an email.

The Ahnentafel Numbering System

Ahnentafel numbering assigns the number 1 to the subject of the genealogy and follows a strict formula for numbering his or her ancestors. The basic numbering system is simple but very powerful. Each father’s number is the child’s number times 2. The mother gets the child’s number times 2 plus 1. So, the subjects father will be number 2 (1 X 2 = 2) and his mother will be number 3 (1 X 2 + 1 = 3). The paternal grandfather will be number 4 (2 X 2 = 4) and the paternal grandmother gets number 5 (2 X 2 + 1 = 5). The maternal grandfather is number 6 (3 x 2 = 6) and the maternal grandmother 7 (3 x 2 + 1 = 7) .

For example, if you were writing your own Ahnentafel, the format would look like this:

1. you
2. your father
3. your mother
4. father’s father (your paternal grandfather)
5. father’s mother (your paternal grandmother)
6. mother’s father (your maternal grandfather)
7. mother’s mother (your maternal grandmother)
8. father’s father’s father
9. father’s father’s mother
10. father’s mother’s father
11. father’s mother’s mother
12. mother’s father’s father
13. mother’s father’s mother
14. mother’s mother’s father
15. mother’s mother’s mother

By convention, terms like great grandfather and great-great grandmother are not used in interpreting Ahnentafels. Instead, the relationships might be described as the subjects father’s mother’s father in the first instance and as the subjects mother’s mother’s father’s mother in the second. After all, you have eight great-great grandmothers but only one mother’s mother’s father’s mother.

Unfortunately, real Ahnentafels usually don’t specify the relationships in the list. This partial Ahentafel of President Barack Obama is an example of what you are likely to see:

1. Barack Hussein Obama, Jr. (1961)
2. Barack Obama (1936-1982)
3. Stanley Ann Dunham (1942-1995)
4. Onyango Obama (1895)
5. Akumu
6. Stanley Dunham (1918-1992)
7. Madelyn Lee Payne (1922)
8. Obama, of Kendu Bay, Kenya
9. Nyaoke
12. Ralph Waldo Emerson Dunham (1894-1970)
13. Ruth Lucille Armour (1900-1926)
14. Rolla Charles Payne (1892-1968)
15. Leona McCurry (1897-aft1930)
16. Obiyo
24. Jacob William Dunham (1863-1936)
25. Mary Ann Kearney (1869-1936)
26. Harry Ellington Armour (1874-aft1930)
27. Gabriella Clark (1877-aft1930)
28. Charles T. Payne (1861-aft1920)
29. Della Wolfley (1863-aft1900)
30. Thomas Creekmore McCurry (1850-1939)
31. Margaret Belle Wright (1869-1935)
32. Okoth
48. Jacob Mackey Dunham (1824-1907)
49. Louisa Eliza Stroup (1837-1901)
50. Falmouth Kearney (1830-1878)
51. Charlotte Holloway (1833-1877)
52. George W. Armour (1849-aft1890)
53. Nancy Ann Childress (1848-1924)
54. Christopher Columbus Clark (1846-1937)
55. Susan C. Overall (1849-bef1920)
56. Benjamin F. Payne (1838-1878)
57. Eliza C. Black (1837-1921)
58. Robert Wolfley (1834-1895)
59. Rachel Abbott (1835-aft1900)
60. Harbin Wilburn McCurry (1823-1899)
61. Elizabeth Creekmore (1827-1918))
62. Joseph Samuel Wright (1819-1894)
63. Frances A. Allred (1834-aft1880)
64. Obongo
96. Jacob Dunham (1795-1865)
97. Catherine Goodnight (1794-aft1870)
98. John Stroup (c1814-1851)
99. Eliza Jane Clemmons (c1816-1882)
100. Joseph Kearney (c1794-1881)
101. Phoebe Donovan
102. Josiah Holloway (1804-1887)
103. Martha Mallow (1810-1888)
104. William Armour (c1812-aft1880)
105. Sarah Poland (1824-aft1880)
106. John Milton Childress (1816-1866)
107. Nancy Conyers (1823-1860)
108. Thomas Clark (1812-1892)
109. Elizabeth Davis (1822-1900)
110. George Washington Overall (1820-1871)
111. Louisiana Duvall (1826-1855)
112. Francis Thomas Payne (1794-1867)
113. Harriet Bowles (1806-1857)

As this example illustrates, it is not immediately obvious how each person in the list is related to the subject. Fortunately, there are a couple easy ways to convert the numbers to relationships. In these examples, we will find the relationship between Barack Obama and John Milton Childress (number 106 in the list).

A Basic Method for Converting Numbers to Relationships

The first method uses repeated division to get a list of parental relationships. Start out by checking to see is the ancestors Ahnentafel number is odd or even. If it is odd, subtract one and divide by 2 and the relationship will be “mother” so write that down. If it is even, as in the John Milton Childress example, just divide by 2 and write “father” like this:


Repeat the process using the answer we just got. 53 is odd so subtract one, divide by 2 and write “mother.” Now we have:

106/2=53 father
(53-1)/2=26 mother

Continue until you get to 1:

106/2=53 father
(53-1)/2=26 mother
26/2=13 father
(13-1)/2=6 mother
6/2=3 father
(3-1)/2=1 mother

Since we started with the most distant ancestor, we have to reverse the list so it reads:

mother father mother father mother father

Then write a relationship statement like:

“John Milton Childress is Barack Obama’s mother’s father’s mother’s father’s mother’s father.”

Using this formula, you can figure out how any person in the list is related to person number 1.

A list of all the ancestors between President Obama and John Milton Childress can be constructed by matching the numbers found during the divisions to names in the Ahnentafel:

Barack Obama (1) is the son of Stanley Ann Dunham (3), daughter of Stanley Dunham (6), son of Ruth Lucille Armour(13), daughter of Harry Ellington Armour (26), son of Nancy Ann Childress (53), daughter of John Milton Childress(106).

Using Binary Numbers to Convert Numbers to Relationships

Since all the divisions in the method above are by 2, it is possible to simplify the process by using binary numbers.

As before, start with the ancestor’s Ahnentafel number. For this example start with the John Childress’ number of 106.

Next, convert that number to binary. The binary representation of the decimal number 106 is 1101010.

There are decimal to binary converters online that can do the conversion for you. An easy one to access is Google SearchTM. Type “106 to binary” in the search box and click the Search button. The answer will be at the top of the result page.

Now, staring with the leftmost digit, write the Ahnentafel subject’s name which is represented by the first 1. Then continue by writing the word father for each 0 and mother for each 1. The result looks like this:

1 Barack Obama
1 mother
0 father
1 mother
0 father
1 mother
0 father

This time there is no need to reverse the list so, John Milton Childress is Barack Obama’s mother’s father’s mother’s father’s mother’s father.

Counting the digits in the binary number and subtracting 1 shows the number of generations between the two people. In the example, there are 7 digits. Subtract 1 for the subject person and there are 6 generations between them.

If you do want to write the relationship in more conventional terms for some reason, just write the binary digits in a column and writing the generation names beside them. Like this:

1 – subject
1 – parent (1 generation)
0 – grandparent (2 generations)
1 – great-grandparent (3 generations)
0 – 2cd great-grandparent (4 generations)
1 – 3rd great-grandparent (5 generations)
0 – 4th great-grandparent (6 generations)

The number of generations between the two people matches the result we got when we subtracted 1 from the number of binary digits (7-1=6) and we now know that John Milton Childress was Barack Obama’s 4th great-grandfather.

Ahnentafels don’t have to be intimidating. By using the techniques presented here, it is easy to convert even the largest numbers to relationships.

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