Why aren't sda3 and sda4 displayed with fdsik -l?

I wanted to display all my partitions, so I entered "fdisk -l". AFAIK, the format of the device file for a scsi hard disk reads like: sd_whichharddisk_whichpartition.

To my surprise, after hitting "fdisk -l", I got:

/dev/sda1 * /dev/sda2 /dev/sda5

So, I got three partitions numbered 1,2 and 5. Why is there a gap between number 2 and 5 ? How many partitions do I have for sure?