Numbers

1 Ichi
2 Ni

3 San
4 Yon/shi/(yo)
5 Go
6 Roku
7 Nana/shichi
8 Hachi
9 Kyuu/ku
10 Juu
11 Juuichi
12 Juuni
13 juusan
14 Juuyon/juushi
15 Juugo
16 Juuroku
17 Juunana/juushichi
18 Juuhachi
19 Juukyuu/juuku
20 Nijuu
30 sanjuu
40 yonjuu
50 gojuu
60 rokujuu
70 nanajuu
80 hachijuu
90 kyuujuu
100 hyaku
200 nihyaku
300 sanbyaku
400 yonhyaku
500 gohyaku
600 roppyaku
700 nanahyaku
800 happyaku
900 kyuuhyaku
1,000 sen
2,000 nisen
3,000 sanzen
4,000 yonsen
5,000 gosen
6,000 rokusen
7,000 nanasen
8,000 hassen
9,000 kyuusen
10,000 man
20,000 nimam
30,000 sanman
40,000 yonman
50,000 goman
60,000 rokuman
70,000 nanaman
80,000 hachiman
90,000 kyuuman
100,000 juumasu

*2,000-9,000 use "zen" (ex-3,000 sanzen)
*200,000-900,000 use "man" (ex-400,000 yonman)


To help you figure out numbers, think of addition.
198=100+90+8=hyaku kyuujuu hachi
2,981=2,000+900+80+1=nisen kyuuhyaku hachijuu ichi
16,547=10,000+6,000+500+40+7=ichiman rokusen gohyaku yonjuu nana

nihyaku gojuu roku=256
nisen kyuuhyaku hachijuu ichi=2,981