Wie viele Überlebende gab es?

Is there any pattern or system with which I can remember which nouns like this have the plural ending in “en” and which have it end just in “e”? Like…this noun, “Überlebende” is confusing to me. It can be masculine or feminine and it ends in “e” either way, and the plural is the same as the singular. Most German nouns ending in “e” in the singular have a plural ending in “en”. Why is this one different?