n = 2•(99 • 100 : 2) - 99
n = 2 • 99 • 50 - 99
n = 9900- 99
n = 9801
............................
n=2x(1+2+3+...+99)-99
2x(99x100/2)-99=
2x(99x50)-99=
2x4950-99=
9900-99=9801
n=9801
