the whole numbers 2000 to 2999.
http://wiki.answers.com/Q/What_are_all_the_4_digit...

You have 10 choices for the first digit, then 10 choices
http://www.chacha.com/question/whatareallofthe...

You have 5 choices for the first number, 5 choices for the second,
http://www.quora.com/Mathematics/Howmanycombinat...

i take it that the # has 4 digits. there are 6 choices for each digit, so. # of combinations = 6^4 = 1296 < qed.
http://answers.yahoo.com/question/index?qid=201204...
