It seems to slow down, as you increase from:

111..111 11111..111111

and eventually crashes.

I'm guessing there is some kind of grammar parser breaking horribly. There's grammar parsers that have extremely poor performance trying to parse stuff that looks like this. It might do:

search 1 and 111111..11111

search 11 and 11111..11111

...

search 1 and 1 and 11111..111

...

...

...

and google detects that you are DOSing its server.

OK, someone else has pointed out that this is a range search, and google may be protecting CC searches.

Years ago somebody discovered you could Google for credit card numbers that had been left on the web inadvertently, by searching for the right number range. I wonder if that is why it is unavailable.

Do you regularly search for 99999...999999? Sounds like it's unusual to me!