Diophantine N-tuples

Can you explain why a sequence of operations always gives you perfect squares?

DOTS Division

Take any pair of two digit numbers x=ab and y=cd where, without loss of generality, ab > cd . Form two 4 digit numbers r=abcd and s=cdab and calculate: {r^2 - s^2} /{x^2 - y^2}.

Sixational

The nth term of a sequence is given by the formula n^3 + 11n . Find the first four terms of the sequence given by this formula and the first term of the sequence which is bigger than one million. Prove that all terms of the sequence are divisible by 6.

Pick's Theorem

Age 14 to 16 Challenge Level:

* How many different figures can be described as $(4, 0)$?

* What do you notice about $(4,0)$ figures?

* Choose another particular value for $(p,i)$ and explore different shapes.

* Have you tried drawing shapes with the same area?

* What do you notice about those figures whose areas are the same?

* What ways are there of increasing the area by $1$ unit?

* Draw more figures; tabulate the information about their perimeter points ($p$), interior points ($i$) and their areas ($A$).