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'Iff' printed from http://nrich.maths.org/
Take some triangular numbers. Multiply each one by eight and add
one.There is an interesting pattern - can you spot it? Test your
conjecture with some other triangular numbers.
Can you prove that the pattern continues for any triangular
If you are finding it tricky to
construct a proof, an activity is available here which allows you to put a proof we have
written in the correct order. Alternatively, look at the hint for a
visual way of thinking about this problem