the number of URLs on the internet

well, you cannot actually know the number of URLs on the internet
first of all, URLs pop in and out of existence all the time
and then not all URLs are indexed by the search engines

at least, it is possible to know the number of URLs a search engine has in its database

perhaps the search engine publishes its own statistics, but you wouldn't want to trust them too much
you dont have to anyway
one way to know is to use their search engines

we need a query that would return every single page
a query that hits every single item in their database

a OR not-a

if a were a member of a set, then a OR not-a is contains every single member in that set

of course, it doesnt have to be "a"

in google, the syntax would be "a|-a"

it may be different in other search engines, go find out for yourself



idea from searchlores.org