Genealogical numbering systems

(First Generation)
1 Subject

(Second Generation)
2 Father
3 Mother

(Third Generation)
4 Father’s father
5 Father’s mother
6 Mother’s father
7 Mother’s mother

(Fourth Generation)
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