Multiple factorial
Writing functions:
factorialmulti(a, b)
The function definition :
Multiple factorial function: if the value of b=1, the feature is a factorial, when b=2 - double factorial b. Determines the step by which to change the difference between elements, for example:
factorialmulti(17, 3)=17*14*11*8*5*2
factorialmulti(23, 5)=23*18*13*8*3