Hi.
1st of all I need to know if you skipped some values in error, for example a result with j6 = 269?
If the above is true then this is easy.
1. Test I'd the target column is c, if it is then test if the target is withing the start and end rows, if true then result is target row minus 25, notice that these differ only by 25.
If results like j6=269 where skipped deliberately then the same algorithm above still applies, but now instead of only testing for the end you'll test for the end of the partition and return the cell row less the common difference for that partition.
Example if within patition j1:j9 common difference is 25, else if whithin j10:j19 common difference is 19, else if within j20:j29 common difference is 40 and lastly If last row common difference is 30.
More clarity,
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