The only number you have to find out is "N" and there are 10 capitals: Nairobi, Nassau, Naypyidaw, N'Djamena, New Delhi, Ngerulmud, Niamey, Nicosia, Nouakchott and Nuku'alofa. I hope it's clear enough :)
'Gassu69..........Congratulations 'Gassu69' although you did not have to solve it so quick. You have now won a 'CHALLENGE GOLD MEDAL' and even if it is only an honorary award you deserve it. Congratulations again.
These numbers represent the number of sovereign capital cities in the world starting with this letter. E has 0, A has 16 and so on....
(with help from Gossguy)