# Start once, second half is easier

Let a recurrence relation be defined as follows: $a_1=1;\ a_2=3;\ a_{n+2}=(n+3)a_{n+1}-(n+2)a_{n}\ \forall\ n\in N$

Calculate the sum of all values of $$x$$ such that $$a_{x}=x^2$$.

×