3. A non-empty finite set whose sum of the squares of all elements is odd is called a trivial set. If the set $A=\{1,2,3, \cdots, 2016,2017\}$, then the number of trivial sets among all proper subsets of $A$ is $\qquad$ (powers of numbers are allowed in the answer).
Among all the subsets of set $A$, those containing 1 and those not containing 1 (with the same other elements) are grouped together, resulting in $2^{2016}$ groups. Since each group contains exactly one trivial subset, note that the subset $\{1\}$ (paired with $\varnothing$) and set $A$ (paired with $A \backslash\{1\}$) are both trivial subsets, so the number of trivial subsets is $2^{2016}-1$.