Replace page number 17, 18 & 19 with the first three numbers of the sequence you want to use (like 50, 51 & 52 if you want to start at page 50).
Select the three renumbered cells. At the bottom right corner of the selected cells is a tiny icon click & drag that downwards to fill the column with the continuing sequence.
Repeat for column G starting with the last number in column B +1.
More on this technique https://support.office.com/en-us/article/Automatically-number-rows-76ce49e3-d8d2-459b-bd85-ee1d3973e6e6