With thanks to E. Mehmet Kıral:
You asked me this morning to give examples of
distributive numbers and their use.
First let me give the numbers
So after each cardinal number we add the suffix -(ş)er or -(ş)ar according to what kind of a wowel the number end with. As in the case of beş (5) if the numeral ends with a consonant then the intermediate letter ş is not used.
Examples of use:
When somebody is distributing some goods s/he might say Beşer beşer alın. (Each one of you take five (not the jazz song)) or İkişer elma alın. (Take two apples each)
I do not know if it is a grammatical rule (or if it is important) but when the name of the object being distributed is not mentioned then the distributive numeral is repeated as in the first example.
The numeral may also be used in a non distributive problem. If somebody is asking students (or soldiers) to make rows consisting of 7 people each then s/he might say
Yedişer yedişer dizilin. (Get into rows of seven)
Since I am listing everything about these numbers, let me also say that they may be written as 1’er, 2’şer, 3’er etc.
These words also distribute events in time according to how many events happen at any given time.
Bu soruları teker teker çözmen lazım. (You should solve these questions one at a time)
By the way the word tek means single and çift means couple. And the -er suffix may be added to these also.
I believe the repetition in these numerals exists to give the feeling of distribution. Since in any distribution event you give more than one time you say beşer beşer and indicate how many objects you are giving to the first two peope, and the rest is assumed to be the same.
If there is a distribution but if everybody does not get the same amount but there is a certain range then one may say
Birer ikişer aldılar. (They took one or two each)
Üçer beşer geldiler. (They came in groups of three to five.)
I hope this was helpful. It might be long. I am not a linguist but I wrote of everything I could think of.