Dear Pluses and readers,
Finding that the calculator here: a) can't divide numbers like 4 and 6, and b) can't show all prime pairs for numbers like 26, I tried to reverse-engineer it, see why it can't do it, and suggest an improvement. Later, I found you have provided your algorithm (in detail) and it is its second part to blame.
I attach a link to my blog where one can see links to two algorithms of mine (not detailed), on the first of which a friend of mine based his calculator (there is a link to this calculator too). Please, don't be too critical, I'm neither a native English speaker, nor a mathemathician, nor a programmer.