Learn Dutch: Ik heb zestien pennen en zeventien boeken. - I have sixteen pens and seventeen books.

Most of them do! Just like English adds '-teen', Dutch adds -tien (which means ten) to the base number. So, zes (six) becomes zestien and zeven (seven) becomes zeventien. Watch out for 13 (dertien) and 14 (veertien), which change the spelling of the base number slightly.

Why does pennen have a double 'n'?

The singular word is pen. Because it has a short vowel sound followed by a single consonant, you must double that consonant when adding the plural -en. If you didn't double the 'n' and wrote penen, the pronunciation of the first 'e' would change to a long vowel sound.

Why doesn't boeken get a double 'k' in the plural like pennen does?

The singular word is boek. Because it has a combined vowel sound (oe), it doesn't trigger the short vowel spelling rule that pen does. To make it plural, you just add the standard -en to the end without changing the base word.

Is the verb heb only used with ik?

Yes, heb is the specific form of the verb hebben (to have) that goes with ik (I). If the sentence was about someone else, like 'he has' or 'the woman has', you would use the form heeft instead.