The solution lies with using Excel's array feature to traverse a data list automatically and extract missing sequential numbers, even if the number list is out of order.

Microsoft Excel's new dynamic array functions make complex calculations easier than ever before.

Learn Excel’s Sequence function to generate numbers, dates, and custom formats effortlessly. Work smarter and faster with this guide ...

You can sum a series of numbers in Microsoft Excel manually by typing in a simple formula, or automatically with a tool.