There are different words for the number of people.
Sentences Business Conversation
Colloquial Daily Conversation
The number 1 is pronounced Ichi, “one” is pronounced Nin, and one is pronounced Hitori instead of Ichinin. This may be because it is difficult for a Japanese person to pronounce one person.
The number 2 also sounds irregular like the above. 2 is pronounced ni, 「2人」 is pronounced futari, not ninin.
The number 4 also sounds irregular like the above. 4 is pronounced yon, The four are pronounced yonin, not yonnin.
Pieces
There are different words for the pieces, too.
Sentences Business Conversation
Colloquial Daily Conversation
1個
いっこ
i k k o
1つ
ひとつ
hitotsu
The number 1 is pronounced ichi, and ”「1個」 is pronounced nin, One pronounces hitotsu, not ichiko. This may be difficult for Japanese people to pronounce ichiko.
2個
にこ
n i k o
2つ
ふたつ
hutatsu
The number 2 also sounds irregular like the above.