In the limit you get the sum of an infinite geometric series. What about an infinite product (1+x)(1+x^2)(1+x^4)... ?

A circle is inscribed in an equilateral triangle. Smaller circles touch it and the sides of the triangle, the process continuing indefinitely. What is the sum of the areas of all the circles?

If a number N is expressed in binary by using only 'ones,' what can you say about its square (in binary)?

Challenge Level

Evaluate the following:

$67^2$

$667^2$

$6667^2$

$66667^2$

What do you notice?

Can you convince someone what the answer would be to (a million
sixes followed by a 7) ^{2} ?

The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the
NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to
embed rich mathematical tasks into everyday classroom practice.

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NRICH is part of the family of activities in the Millennium Mathematics Project.

NRICH is part of the family of activities in the Millennium Mathematics Project.