Arko and Special permutations

Arko is very fond of permutations. He can easily calculate the number of n length permutations. (In which permutations there contained n numbers from 1 to n are called n length permutations. (2, 1, 3, 4) is called a 4 length permutations.). So his teacher give him a tricky problem on permutations. He has to calculate the number of n length permutations where r specific values will be in same order.


This is a companion discussion topic for the original entry at https://toph.co/p/arko-and-special-permutations