It can be called a research article, but for this name lacks depth of results.
It may be useful as an expository for students.
I prefer open access journals, but for this particular article, it's OK for me to publish it in a closed access journal. However it is necessary that publishing in a journal will not forbid me to put a copy of my article in a book I am writing. Publication fees are bad for me, but I may consider to publish even in a journal taking publication fee.
Which journal you may suggest?
I've already sent it to a few journals and it was rejected.