No existing pages in Google index

[visibilitysk]

I have a real estate portal. I have a few categories - for example: flats, houses etc.

Url of category looks like that:

mydomain.com/flats/?page=1

Each category has about 30-40 pages - BUT in Google index I found url like:

mydomain.com/flats/?page=1350

Can you explain it?  This url contains just headline etc - but no content! (it´s just generated page by PHP)

How is it possible, that Google can find and index these pages? (on the web, there are no backlinks on these pages)

thanks

[AlanBleiweiss]

Without knowing the site there could be any number of potential causes.  On-site search? internal links?  Original site set up that has since changed but had been crawled before a change?  As for other issues and not having current pages indexed, I'd look at the robots.txt file, page header signals (noindex as one example, canonical tag usage as another)...