Homework Statement
Let S(n,r) denote the number of elements of A_n of rank r. Then S(n,r) satisfies the recursion S(n,r)=(n-r)S(n-1,r-1) + S(n-1,r) Verify this formula for n=4 and r=0,1,2,3,4, using the values
S(3,0) = 1
S(3,1)=3
S(3,2)=1
Homework Equations
The Attempt at a...