I would like to create a list of numbers (ie: from A2:A25). Then have a field
that a user can put in a number to indicate the number of rows to sum into a
third field. Ie: input the number 3 to cell C1. The sum of cells A2:A4 would
be returned into the result field, say, cell C3.

Assume that A2 will always be the first number in the sum equation. If the
value in C1 were changed to 4, the result in C3 would be 19 since it would
include the number in the range. See sample below. Any clues??

A B C D
1 3
2 6
3 9 16
4 1
5 3
6 7
7 4