No it is not.
Depends on what you mean by "Backdoors". Usually that means that the
coder has purposely installed bit of program which allow someone in the
know to get into that program, or that computer, to do what theywish.
Linus has a certain level of defence in that the source code is open for
anyone in the world to see, and to report on kind of code. (That they
can of cours does not mean that they will look, and if they look and
find it, they may just keep quiet and use the backdoor themselves. Of
course that may be an addition disincentive to install such backdoors
since they have no idea who is going to be able to use them, not just
the coder. )
In closed source programs it is harder to find such backdoors, the
disincentives are much less. But again that does not mean that the coder
do install backdoors.
Now you could mean "backdoor" as a bug, unintended by the coder, which
allows access. That also means it is far harder to count them, since you
have to find them to count them.
So all in all, your question makes not much sense.