# Mathspp Blog

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##### Base conversion in Python

This article shows how to do base conversions in Python with the built-in int, how to write integer literals in other bases, and how to do base conversions in general.

##### TIL #017 โ symmetrical indexing with bitwise inversion

Today I learned about the symmetry in indexing from the beginning and end of a list with the bitwise invert operator.

##### Problem #029 - hidden key 2 ๐๏ธ๐๏ธ

This problem is a step up from Problem #028 - hidden key. Can you tackle this one?

##### Problem #028 - hidden key ๐๏ธ

There is a key hidden in one of three boxes and each box has a coin on top of it. Can you use the coins to let your friend know where the key is hiding?

##### Problem #024 - hats in a line

Some people are standing quiet in a line, each person with a hat that has one of two colours. How many people can guess their colour correctly?

##### Twitter proof: size of the set of subsets of a set

Let's prove that, if a set has size $$n$$, then that same set has exactly $$2^n$$ subsets.

##### Problem #005 - number me right

This problem is a really interesting problem I solved two times. The first time I solved it I failed to prove exactly how it works... then some years later I remembered the problem statement and was able to solve it properly. Let's see how you do!