Return only numbers directly after specific substring

Hi
Sorry, I don't see de range 1-4 digits.
The array formula is

Formula:

=RIGHT(MID(A1,SEARCH("RX",A1,1),COUNT(VALUE(IFERROR(MID(J9,{1,2,3,4},1),"")))+2),COUNT(VALUE(IFERROR(MID(J9,{1,2,3,4},1),""))))

Regards