D=4+12+24+40+...+19404+19800
4+12+24+40+...+19404+19800=???
4+12+24+40+...+19404+19800
4+12+24+40+...+19404+19800
B=4+12+24+40+...+ 19404+19800
A=4+12+24+40+...19404+19800
a=4+12+24+40+...+19404+19800
A=4+12+24+40+...+19404+19800
Tính:
4+12+24+40+...+19404+19800=?
