I want to sequentially number a list ignoring blanks

I have a column of week numbers but some gaps in the list (e.g. the job is complete and so I do not want to reference it) I am trying to create a list of jobs by week number. I need to sequentially number jobs to then use Vlookup e.g. job1-week1 job2-week1 etc to display be week.

I can work out to number the list ignoring the blanks but then resetting to 1 with each new week?

Please help its driving me mad!Workbook1.xlsx

if I have a list of week numbers I need to concatenate a number to the weeknumber to then look it up and display each weeks work in a separate column on a separate sheet. Without gaps this works if in cell a2 =if(a1=a2,b1+1,1) (assuming column a is the weeknumber) however when there are gaps in the weeknumber column I get repeat numbers which I then cannot vlookup. eg if weeknumber 6 has 10 rows, 2 of those rows might show a blank weeknumber (as we have finished the job)so ill end up with 1-6,2-6,3-6,then if there is a gap it goes back to 1-6. I only want to reset to 1 when the weeknum changes and ignore the blanks