Long numbers (i.e. those with more than one element) are rarely written out in full. In practice, complex numbers are rarely written fully except on cheques, and figures are used in written German more often than is usual in English.
Numbers higher than a thousand are written with spaces every three digits - not with commas as in English, i.e. Germans would write 123 678 and not 123,678 as in English.
Vocabulary 3: Larger numbers
123 678 hundertdreiundzwanzigtausendsechs-
hundertachtundsiebzig
1 000 000 eine Million
2 000 000 zwei Millionen
10 000 000 zehn Millionen
5 276 497 fünf Millionen zweihundertsechsundsiebzigtausend-
vierhundertsiebenundneunzig
1 000 000 000 eine Milliarde
2 000 000 000 zwei Milliarden
10 000 000 zehn Milliarden
Explanation
1) The numbers eine Million and eine Milliarde are treated as separate nouns. They thus have a plural ending wher necessary - i.e. drei Millionen fünfhunderttausend.