



 
Hi Gary, Look at my response to Judy when she sent a similar question. She had 10 digits to choose from where you only have 4. In her case she had $10^6$ possibilities, too many to list. You have $4^4 = 256$ which is easier to deal with. To list them start with 1111, then 1112, 1113 and 1114. Then 1121, 1122, 1123, 1124, 1131, and so on. I hope this helps,  


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