Incrementation of the value of variable

Have you tried doing it?

There is a commando called print that can be used to output, among other things, the output of variables. Read the documentation.

should be

variable A equal 5
run 10000
variable A equal $A*5

The syntax ist:
$A for parser
v_A for runtime variable

Immediate Evaluation of Variables:
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There is a difference between referencing a variable with a leading $ sign (e.g. $x or ${abc}) versus with a leading “v_” (e.g. v_x or v_abc). The former can be used in any input script command, including a variable command. The input script parser evaluates the reference variable immediately and substitutes its value into the command. As explained in Section commands 3.2 for “Parsing rules”, you can also use un-named “immediate” variables for this purpose. An variable reference such as $((xlo+xhi)/2+sqrt(v_area)) evaluates the string between the parenthesis as an equal-style variable.

https://www.cfdem.com/media/DEM/docu/variable.html