How to generate auto sequence number for repeating sets of array

Can anyone guide me how to generate sequence number for n numbers of digits present in a excel column in the form of repeating arrays of "2", "1" and "4". For Example if the cell Range A2:A6 is having cell value as "2" then it should have a sequence of 1,2,3,4,5 likewise for A7:A12 having cell value as "4" then it should have a sequence of 1,2,3,4,5. For now i am able to generate the sequence number for the first set of array for each digit value "2" "4" and "1" by using COUNTIF like COUNTIF(A$2:A2,A2). The solution i am looking into is that for every set of array it should start the sequence from 1 and end at the total count of the digit value for that set of array. Auto-Sequnce-Number.xls is attached herewith for reference.

Thank you Glenn for your answer and yes you are right B17 should read 1 and not 5. The solution you provided is working fine for the given scenario but their is slightly misinterpretation of the input fields. Actually the column "C" contains the sequence number generated by me by using COUNTIF which is not the result i want. The result i want is that the formula take input value from column "A" and return the sequence number as result in any desired column of excel.

My sincere apologies. The solution provided earlier is working fine. Thanks a lot for your help.