Setting range to every nth cell in a column

I am trying to loop goal seek every 29th rows in Column D starting with row 15.

With a lot of trial and error and web searching, I figured out how to set the goalseek function to the proper variable cells, but now I'm stuck at how to efficiently set my range.

This is what I have:

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I can of course manually set my range to all the individual cells (D15, D44, D73, D102, etc) all the way to the final cell, D2886, but that is both tedious and far too static. I need to be able to change the range criteria more easily to accommodate future updates to the page.

Any suggestion is appreciated. Thanks!

Thank you, but this seems to be having some problems. It says "Run-time error '13': Type mismatch". GoalSeek is a bit picky about what it will cooperate with. So far cll and range are the ones it seems to like the best

Hmm, still no luck. It really is a pretty uncooperative function. I've found a few ways to make it work in different circumstances (making the value and changing cell into dynamic ranges took some trial and error), but creating a custom range that it will play nice with is proving extra tricky.