1991 minus half of it, then minus the remaining 1 / 3, then minus the remaining 1 / 4... And so on, finally minus the remaining 1 / 1991

1991 minus half of it, then minus the remaining 1 / 3, then minus the remaining 1 / 4... And so on, finally minus the remaining 1 / 1991

=1991-1991 * 1 / 2-1991 * (1-1 / 2) * 1 / 3-1991 * (1-1 / 2) * (1-1 / 3) * 1 / 4 -... - 1991 * (1-1 / 2) * (1-1 / 3) * (1-1 / 4)... 1 / 1991 = 1991 * [1-1 / 2 - (1-1 / 2) 1 / 3 - (1-1 / 2) (1-1 / 2) 1 / 4 -. - (1-1 / 2) * (1-1 / 3) * (1-1 / 4)... 1 / 1991]