[tex]\boxed{1+3+5+...+\big(2\cdot n-1\big) = n^2}\rightarrow formula\\
$ \\ \\ $
A=2+6+10+...+4026+2015 \\ \\ A = 2\cdot (1+3+5+...+2013)+2015 \\ \\ A = 2\cdot \Big(1+3+5+...+\big(2\cdot 1007-1\big)\Big)+2015 \\ \\ A = 2\cdot 1007^2+2015\\ \\ A = 1007^2+1007^2+1007+1008 \\ \\ A = 1007^2+1007\cdot (1007+1)+1008 \\ \\ A = 1007^2+1007\cdot1008+1008 \\ \\ A = 1007^2+1008\cdot(1007+1) \\ \\ A = 1007^2+1008\cdot 1008 \\ \\ A = 1007^2+1008^2[/tex]
