One of the first Japanese concepts we get in touch with when starting kendo are the numbers, which are quite commonly used for counting during warming ups and different exercises. The next table summarises the numbers from 1 to 10 in both Japanese and English:
As the chart indicates, some numbers have various readings. For instance, 4 can either be 「Shi (し)」 or 「Yon (よん)」, 7 can either be 「shichi (しち)」 or 「nana (なな)」and 9 can be read as 「Kyu (きゅう)」or 「Ku (くう)」. Basically, both pronuntiations are acceptable up to 10. However, past ten, the reading is almost always 「Yon (よん)」 and 「nana (なな)」.
In the next video you can check the pronunciation of the first 10 numbers in Japanese: