BTW, you'll note our post's title says (Journey Into) Unknown Worlds.
The indicia says Unknown Worlds, and as of the next issue, until the end of the run, it would read Journey into Unknown Worlds.
Also, this is the first issue of the title!
The book had been Teen Comics, and before that, All-Teen Comics.
Comics publishers did this because they were notoriously cheap, and each new comic title (classified by law as a new periodical) required a new second-class mailing license for subscriptions.
So publishers tried to keep the numbering of already existing titles, modifying the name just slightly, to keep the already paid license!
But the postal authorities caught them, and Atlas had to pay for a new second-class license and restart the numbering!
So, technically, this was #1, and as of what would have been #39, the numbering restarted with #4!