arithmancy
[ ar-ith-man-see ]
/ ˈær ɪθˌmæn si /
noun
divination by the use of numbers, especially by the number of letters in names.
Also
a·rith·mo·man·cy
[uh-rith-muh-man-see, ar-ith-] /əˈrɪθ məˌmæn si, ˈær ɪθ-/.