Give a man a fish, he eats for a day... Teach a man to fish, he eats for life...
that 1.6 x crop factor- the equation works backwards as well. So, if you have a lens on a crop- and you want to see what it is similar on a full frame-multiply by 1.6. To take a lens, like a 24-105 on a full frame and figure out its crop equivalent - divide the numbers by 1.6.
18-55 = 28- 88. So, a 24-70 is going to be a little shorter. A 24-105 is similar to a 15-65. The 24-70 is referred to as "the brick" - something about its weight. I'd recommend a 24-105 instead- especially if weight is a concern ( you need to be comfortable unless you are putting it always on a tripod ).
A 17-40 on a full frame is quite WIDE. It'd be like a 10-22 on a crop (approximate ). WIDE- or by some people's definitions- ultra-wide.