Triangular array read by rows: T(n,k) is the number of elements x in {1,2,...,n} such that |(f^-1)(x)| = k over all functions f:{1,2,...,n}->{1,2,...,n}; n>=0, 0<=k<=n.

A210457

Triangular array read by rows: T(n,k) is the number of elements x in {1,2,...,n} such that |(f^-1)(x)| = k over all functions f:{1,2,...,n}->{1,2,...,n}; n>=0, 0<=k<=n.