hmm...interesting request.

I think that you could do something like:
shared stringvar array permit;
shared numbervar lastIndex;
shared numbervar maxSize;
shared numbervar lastPermit;

if lastIndex + 1 >= maxSize then( // check and make sure the array is big enough
maxSize := maxSize + 10;
redim preserve permit[maxSize]
);

if {table.field} = lastPermit + 1 then( //sequential
lastPermit := {table.field};
)
else(
permits[lastIndex] := permits[lastIndex] + "-" + totext(lastPermit, 0, "");
lastIndex := lastIndex + 1;
permits[lastIndex] = totext({table.field}, 0, "");
lastPermit := {table.field}
);

this would be in the details section.

in the report header, or the group header, depends on what you have, you would have a reset formula like:
shared numbervar lastIndex := 0;
shared numbervar maxSize:=10;
shared stringvar array permit;
shared numbervar lastPermit := -1;
dim permit[maxSize];

in the report or group footer, you would need a display routine, to mimic what you had as a sample (also set this to Can Grow to accommodate an unknown number of lines):
shared numbervar lastIndex;
shared stringvar array permit;
local numbervar cur;
for cur=1 to lastIndex do(
permit[cur] + chrw(13) + chrw(10);
)


some of my syntax may be off, this is just off the top of my head. Dimensioning an array may be different as I have never done this myself. Arrays in Crystal are not overly helpful, but in htis case I think that they could be the solution.

The general idea is to create an array of strings. Store the first value of a 'run'. Then every time the next permit is in sequence update a counter. Where the numbers are not sequential, the write the range to the array and set the array for the next range.

It's an idea, hopefully it will lead to a solution.