In Welsh we use the singular after the lower numerals. For larger numbers (over ten-ish, say) it is traditional to use 'numeral + o + plural noun', but you can also stick with 'numeral + singular noun' if you want to. Remember the mutation after o:
- naw deg o feiciau (or naw deg beic)
- ugain o gŵn (or ugain ci or dau ddeg o gŵn or dau ddeg ci)
With the use of Welsh to teach Maths, the number and singular form is becoming more common because of its simplicity.