What is the sum of the series [math]1+ 1 / 2 + 1 / 3 + 1 / 4 + 1 / 5 ...[/math] up to infinity? How can it be calculated?
If [math]3![/math] is [math]3 \times 2 \times 1[/math] then what is [math]1.5![/math]?