I've worked out that there are 9 different possibilities for the first 3 numbers, I think 15 for the first 4 (please tell me if I'm wrong, but only give a clue not the answer) and 16 for the first 5.

I just have no idea how to incorporate the idea that although a number is a possibility for example statement 3 or 4, it may not be possible for the 7th statement (Number formed by the first 7 digits...). Nor how I can check these possibilities and see if all their numbers are different.

No calculator, (yes a spreadsheet would be great, but no

), and no A-level maths or higher.

I need to find a number but preferrably how many numbers that correspond to these rules exist.

Please help me out with clues.

Thanks.