Hello serena,
this has probably what to do with the order how the SEF URLs were generated. You can either try to delete the URLs and let JoomSEF regenerate it or adjust them manually in JoomSEF Control Panel.
The situation you describe may occur e.g. when you have multile places where you point to your frontpage, but each with different Itemid. Then each of such links may be given an extra number, such as 2, 3, ... . Then any pagination links on your forntpage, will continue in this numbering, so then your second page may have number 4, returning link to page 1 from page2 may have number 5, etc.
Sometimes, depending on the order how the links are created, the order of the numbered links may become unlogical, still you can adjust them manually.
Best regards,
ARTIO Support Team