Vier (4) - tis one hard to remember lol
Fuenf (5) - properly fünf
Zwoelf (12) - properly zwölf
Fuenfzehn (15) - properly fünfzehn
Zwozig (20) - I wonder if Zweizig would be interrupted as 20. Seems that 'zwo' seems to be used in place of Zwei at times to avoid confusing people.. Probably foreigners lol.
For the most part German numbers seem pretty logical and seem to follow the same convention style as English numbers. I.e. 15 in English is Fift-Teen, rymes with 5th (fifth, Viertel) a fraction and teen being a fairly standard suffix for any thing between ( > 10 && < 20 ). So Siebzehn makes sense for Seventeen. Its more or less 'Seven Ten' which is basically what a 17 is. Or maybe it could just be my backwards mind that finds this all so logical ! hehe I dunno.
Larger numbers seen to follow a similar style but with a und (and) in the middle and changing suffixes as you got, teens, twenties, thirties and so on. But each comparable German suffix seems to end in 'zig' except for Dreissig (dreißig, thirty). Much like how in English many of then have a 'ty' suffix often preceded by an r or ir. Fourty "four'ity" (Vierundvierzig), Seventy (Siebundsiebzig), or Fifty (Fuenfundfuenfzig). Quiet logical imho.
Sechhundertzweiundzwanzig (626) looks about right to me aside from being a mouth full but who says I know any thing. Six hundred Two and Twenty - logical.
It seems while we use a decimal point . In German a comma , seems to be used and pronouced. I wonder how 600,400.01 would be spoken if 3.04 would be like 'Drei Komma null vier'. I think thats some what grammatically correct. 'Komma' always seems to be capitalized, the first word being capitalized the way I wrote it is probably an English'ism. I've yet to learn much for German grammar and punctuation. Instead concentrating on basic spoken communication and reading. I'll worry more about it when I have a rough understanding of how words work out, then I'll worry more about sentences and phases.
So far though the only languages I know my way around well is C and English +S lol sorry to say but I think its in that order :-P