I like that first number() approach; it is KISS.
The comment about a "less brittle" way is very apropos in that the returned URL (if that indeed is what is returned by the GET) on a mobile pone is apparently quite different than what i saw online and offline.
I could see that selecting page+ started chain of actions, and an apparent loading of new visual page.
Seems that the "fixed" stuff gets re-loaded, and then the part for the new image gets parsed by the browser and then i see "page error" and some kind of URL error.
Hard as all hell to see as the font is in the region of 4 points.
Naturally, i do not understand the "syntax" for squat with all those slashes scattered around..
I do not mind blindly doing a copy,and i will do so and try that out online and offline; mobile trys are almost impossible as i have to beg for use.