It certainly would be a boring hobby for most people but, while I was on my extended vacation, quite often I would arrange for a long, comfortable stay in solitary/isolation/segregation/"the hole". I had to be careful or the shrinks would see that I liked it. (Which, one day, they eventually did. But that's another story.)

While in my solitude, I would often work on mathematics for the simple fun of doing something unusual. There is one cell where I was "housed" that bears the calculations of what the latitude and longitude are for the prison. In that cell, I was given a pen filler (a normal pen with the pen barrel removed) and normal writing paper. Often, I would use up my allotment of paper so I began writing on the walls. I'm sure, today, it has all been painted over, but you get the point.

I had only a booklet of sight reduction tables (called the S Tables), a known length of paper (8 1/2 by 11 copy paper), the sunlight that came through some holes in the plated-over window of the cell, and a couple C/O's who would go home and sync their watches with the local news radio for a "to the second" time tick. Using just the sunlight angles on the floor/wall, the sight reduction tables, that pen and paper, and an exact time tick from the C/O, I would calculate my location to within a square mile or two. It would take me weeks to get that accurate because I could only get a good time tick when the C/O would come by. Later, back in general population, I checked the library's world almanac to prove my accuracy. It was a fun project.

Another project I did using just that flimsy pen and paper, was to calculate unusual numbers to a precision well beyond what an 8 or 10 digit calculator would return. For example, square roots. Try finding the exact number that, when multiplied by itself, equals the year 2001. Get a calculator. Now, get that number to 20 decimal places. By checking 44.7, 44.8. 44.75, 44.74, 44.73, 44.735, and on and on for 20 decimal places. I did that on paper.

Then, there are logic puzzles. Many of them are very simple so I'll copy one here. But some of the one's I did took months to solve due to their complexity.

In a certain bank, the positions of cashier, manager, and teller are held by Brown, Jones, and Smith, though not necessarily respectively.

The teller, who was an only child, earns the least. Smith, who married Brown's sister, earns more than the manager.

What position does each man fill?

Brown cannot be the teller because he had a sister. Smith cannot be the manager because he earns more than the manager. Gimwinkle cannot be sane because he finds these types of puzzles fun.

The field of mathematics can be as simple to play in as adding two numbers together or as complex as proving Fermat's Last Theorem (look up Andrew Wiles... Let me check if I remember his name correctly... Ha!!! I was right!)