that's the way it is in german norgeskog, after you get past the teens (why does so much clear up and get easier after the teens?
)
for instance:
eins, zwei, drei, vier, funf, sechs, sieben, acht, neun, zehn, for 1 to 10.
then elf, zwolf, for 11 and 12, (see, they're oddballs)
then dreizehn (3 - 10, or 13), vierzehn (4 - 10 or 14), funfzehn, sechszehn, siebzehn, achtzehn, neunzehn, zwanzig, for 15 thru 20.
then it gets easy, just the first 9 numbers and the decade marker. such as 21 is einsundzwanzig, or 1 and 20. 35 would be 5 and 30, or funfunddreizig.
it's very easy...