There are 10 numbers in all including 0. The first space can be filled in 9 ways (as we have to exclude 0). The second through sixth spaces can be filled in 10 ways as 0 can be included.
Totally, 9 x 10 x 10 x 10 x 10 x 10 or 9 x 10^5 digits can be formed if repetition is allowed.
10,000
120 There are 6 digits in total. The numbers with 3 digits, with all digits distinct from each other, are the permutations of the 6 digits taken 3 at a time, and therefore there are 6*5*4 = 120 of them.
36
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The number 1234567890 can create about 39 of 40 4 digit numbers.
pizza
There are 5 numbers of 1 digit, 25 numbers of 2 digits, and 75 numbers of 3 digits. This makes 105 numbers in all.
2,401
Assuming all 45 digits are different (which they will not be if they are ordinary integers), then 456, if repetitions are allowed. That is 8303765625. If repetitions are not allowed then the number falls to 45*44*43*42*41*40 = 5864443200
10,000
5^4
27 three digit numbers from the digits 3, 5, 7 including repetitions.
504
543210
64 if repetition is allowed.24 if repetition is not allowed.
The number of six digit numbers that you can make from ten different digits ifrepetitions of same digit on the six digit number is allowed is 1 000 000 numbers(including number 000 000).If no repetitions of the the same digit are allowed then you have:10P6 = 10!/(10-6)! = 151 200 different six digit numbers(six digit permutations form 10 different digits).
If repetition of digits isn't allowed, then no13-digit sequencescan be formed from only 5 digits.