string editing suggestions

["Graves, Chuck" <cgraves@xxxxxxxxxxxxxx>]

I have a need to edit/validate a 23 character field, with the following:

1) numeric only... easy enough with TESTN OP Code

2) minimum of 6 characters ... easy enough by finding the position of
the first blank character etc.

3) testing for non-repetitive characters (i.e. maximum of x number of
the same digits keyed...not necessarily consecutive) AND, x is based on
HOW MANY characters were keyed within the 23 character string.

Anyone got any slick routines for #3

TIA

Chuck Graves
Rodda Paint Co.