Translation:I no longer remember those twenty-eight cities.
It should be accepted, but it is not that simple to call it not proper English.
In this sentence, the form "can not" should not be accepted, because it has a different meaning. -> "Můžu si nevzpomenout/nepamatovat těch 28 měst."
Opinions in different references vary. I did consult several of them before my previous answer. Most say it is a less common spelling with the same meaning. This one has links to several references https://www.dailywritingtips.com/cannot-or-can-not/