... the clue I have been told is in the sequence - have tried all the obvious alphabetic, and numeric answers - any other ideas ?

4251... what does it mean?

What do you mean by "the clue?" The clue to what?

If the number 4251 is separated into individual digits 4, 2, 5, and 1 it could be the start of the following sequence: 4, 2, 5, 1, 6, 0, 7, -1, 8, -2,.