One example to get 33 for [1, 2, 3, 4, 5] is

  1 + 2, 3 + 4, 3 + 5, 7 + 8

Just generating all permutations of linear summations is not enough.

Thank you a lot for your feedback! But yesterday when I tried that code without impact to \n it did not work properly. It just outputed the strings those were separated into two string. It seemed like as \n considered like new string sign. That, like I thought, caused the same issue I wrote above. But today I deleted the part with \n and code works so thank you!

Leave the "\n" alone, only replace the vowels.