Nope, because even numbers are observed. The length itself is an observable fact.
Numbers are not observed. We assign numerical value to things we observe. The numerical value itself is apriori.
What you are arguing is really irrelevant to this topic. SCP said logic proves everything and rules all, while at the same time deny the possible existence of other realities. I merely refuted that statement and said logic without observation is just nonsense in his theory of one reality.
But the very statement "logic without observation is nonsense" is an apriori statement. Prior to applying empirical principles to observation, one must first have these principles of empiricism, yet these principles are themselves apriori. To say that anything can be derived from observation, one must first believe that it is possible to derive truth from observation. But this belief is apriori to observation itself, hence there was a point in the empirical methology when logic is without observation, yet this logical premise without observation still holds for the empiricist as it is an indispensable premise.