Lots of ones

Is any of the numbers 11, 111, 1111, 11111, ... a square number?

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What is the sum?

What is \(\displaystyle\frac{1}{\sqrt{1}+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+...+\frac{1}{\sqrt{15}+\sqrt{16}}\)?

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Advent calendar 2019

Sunday Afternoon Maths LXVII

Coloured weights
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Advent calendar 2018

Sunday Afternoon Maths LXVI

Cryptic crossnumber #2

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