Heres an algebraic riddle that I can't solve! HELP!?

[tjflorida711]

A brick wall has a bottom row 49 bricks long, each row up has two less bricks then the one below it. The top row has 3 bricks. The wall is one brick thick....So its like a triangle.

I thought I could solve it using geometry taking 49 x 24x 1/2 but for some reason it didn't work. How do you solve this algebraically?

 

[TheSicilianSage]

24 .............. 24 ... 24
? (2k+1) = 2 ? k + ? 1 = (24)(25) + 24 = 624
k=1 ........... k=1 .. k=1