The Igbo are a Nigerian ethnic group whose homeland is south of Yorubaland in West Africa. Like the traditional Yoruba numbers, the traditional Igbo numbers are vigesimal and based on counting cowrie shells. Unlike Yoruba numbers, Igbo numbers use bundles of six as the unit of counting with cowries. This collective counting created a second counting sequence: in addition to a sequence for counting things one by one, a second sequence counted units of six one by one, and the resultant values were understood as multiplied sixfold (that is, three cowrie bundles would be understood as having the value eighteen). Like Yoruba numbers, Igbo numbers can be formed in an unusual number of alternative but well-formed ways. This flexibility does not represent a lack of lexicalization, the process whereby names for numbers become standardized in speech. Rather, like the Yoruba people appear to have done with their traditional numbers, the Igbo people may conceive of their traditional numbers as arrays of combinatorial possibilities. This conceptualization suggests an influence of the material form used to represent numbers, the bundles of cowrie shells and the collective method of counting them.