The given expression is $$(10^{4n^2 + 8} + 1)^2$$.
The expression will be of the form $$(10000....1)^2$$
Any number of the form 1000(x times)1 will be of the form 1000(x times)20000(x times)1.
For example $$1001^2$$=1002001
So, the sum of the digits will always we 1+2+1=4