Hi Mike,
"When I create a pattern 1,2,3 and then try to drag down to expand it I only copy the last number in the series"
I think your error may have been to enter 1, 2 and 3, then with only the cell containing 3 selected to drag down to fill the rest of the rows. For an arithmetic series, Numbers needs at least two seed values selected to determine the interval of the series. In this table, the first three values were entered in cells B2-B4 and cells C2-C4. B4 and C4 were then selected, and the yellow fill handle dragged down to fill the values into the rest of the rows in these two columns.

Note that the number series (an arithmetic progression with an interval of 1) did not continue, as only one 'seed' value (3, in cell B4) was selected to seed the series. What follows is an arithmetic series, but one with an increment of zero.
But in column C, the alpha-numeric series did continue, even though only a single 'seed' value ("A3" in cell C4) had been selected. A text string that ends with a number (of one or more digits) will produce a series where the part before the number remains the same, and the number at the end of the string progresses with an interval of 1.
Intervals other than 1 are also possible. In this case, at least 2 cells must be selected for either the number or the alpha-numeric series.

Some other series with a default increment are the three in the table below (Column D is another example of the alpha-numeric series above).

Regards,
Barry