\[\begin{array}{l}
A = 1 + 5 + 9 + 13 + 17 + .... + 445 + 449\\
Ta\,\,nhan\,\,thay\,\,\,tong\,\,tren\,\,gom\,\,cac\,\,so\,\,cach\,\,nhau\,\,4\,\,don\,\,vi.\\
So\,\,\,\,cac\,\,so\,\,hang\,\,cua\,\,\,tong\,\,tren\,\,\,la:\,\,\,\frac{{449 - 1}}{4} + 1 = 113\,\,\,so\,\,hang.\\
\Rightarrow A = \frac{{\left( {449 + 1} \right).113}}{2} = 25425.
\end{array}\]