Sentence:  With regard to the Danish numeral-words founded on the <WSD>vigesimal</WSD> system of numeration, it must be admitted that here the explanation fails which has been given for the divergence of the forms representing 70, 80 and 90 from the forms representing the lower numerals of 10 in the case of some other languages, since in the present case the forms for 50 and 60 also depart from the decimal system; ... 
Meaning of the word marked with <WSD> tags:  To the base twenty. (from mid-17th c.)