If n cards are dealt from a well shuffled deck, how likely is it that all 4 suits
will be represented by at least one card?

The following Excel spread sheet image is based on one million Monte Carlo trials computed with the FORTRAN program that I wrote in July, 2006.  The source code is pickcard1.for.  These results agree well with the output of another program in which the exact probability was computed.

The corresponding Excel spread sheet.