Japanese numbers follow two main systems. The basic numbers from one to ten are 一 (いち / ichi), 二 (に / ni), 三 (さん / san), 四 (し or よん / shi or yon), 五 (ご / go), 六 (ろく / roku), 七 (しち or なな / shichi or nana), 八 (はち / hachi), 九 (きゅう or く / kyuu or ku), and 十 (じゅう / juu). Numbers like 4, 7, and 9 have multiple readings, and speakers often choose the alternative reading when the primary one sounds like an unlucky word: し echoes 死 (death), and く echoes 苦 (suffering). Zero is either 零 (れい / rei) in formal contexts or simply ゼロ (zero) borrowed from English.
Larger numbers include 百 (ひゃく / hyaku) for 100, 千 (せん / sen) for 1,000, and 万 (まん / man) for 10,000. Importantly, Japanese groups large numbers in units of 10,000 rather than 1,000, so 100,000 is 十万 (juuman, "ten ten-thousands"), not expressed as "one hundred thousand" as in English. Numbers 11 through 99 follow a simple pattern of tens plus ones: 11 is じゅういち (juu-ichi), and 25 is にじゅうご (ni-juu-go, "two-tens-five"), where the tens digit multiplies じゅう. Some multiples cause sound changes, such as さんびゃく (sanbyaku) for 300 and さんぜん (sanzen) for 3,000.
Japanese also requires counters that match the type of object being counted. The native general counter uses ひとつ (hitotsu), ふたつ (futatsu), みっつ (mittsu), よっつ (yottsu), and いつつ (itsutsu) for one through five, going up to とお (too) for ten, and works for most objects when no specific counter is needed. For people, ひとり (hitori) and ふたり (futari) are irregular for one and two, with さんにん (sannin) from three onward using にん (nin). Flat objects like paper and tickets use まい (mai), long cylindrical objects like bottles and pens use ほん (hon) with sound changes such as いっぽん (ippon), にほん (nihon), and さんぼん (sanbon), and small animals use ひき (hiki) with similar changes like いっぴき (ippiki) and さんびき (sanbiki).