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2022—33rd Annual Field Day
A recursive program that solves the “Tower of Hanoi” puzzle with “3→3” disks.
For a more detailed explanation of the T-shirt, click here. 
  Here is a Java implementation of this program with 3, 6, and 10 discs.

2020—32nd Annual Field Day
A five-dimensional hypercube with 32 vertices.
For a more detailed explanation of the T-shirt, click here. 

2019—31st Annual Field Day
31 is a Mersenne Prime. As of February 2019 only 51 Mersenne primes had been discovered.
For a more detailed explanation of the T-shirt, click here.

2018—30th Annual Field Day
30 is a square pyramidal number: it is the sum of the first four squares.
For a more detailed explanation of the T-shirt, click here. 

2017—29th Annual Field Day
Maximum number of pieces when cutting a pizza 7 times = 29.
For a more detailed explanation of the T-shirt, click here. 

2016—28th Annual Field Day
Euclid’s Proposition IX.36, with n=3, implies that 28 is a perfect number.
For a more detailed explanation of the T-shirt, click here. 

2014—27th Annual Field Day
A cube (volume = 27) progresses towards a Menger sponge (fractal dimension ≈ 2.7). 

2013—26th Annual Field Day
Front: a net for a rhombicuboctahedron.

Back: a rhombicuboctahedron with its 26 faces. 

Here is a video demo that creates a rhombicuboctahedron from its net.

2012—25th Annual Field Day
Prime factorization reveals that only perfect squares have an odd number of factors. 

2011—24th Annual Field Day
A Cayley graph depicting α and β as generators of S₄, which has 24 elements. 

2010—23rd Annual Field Day
Relation between 23, e, and π, and a skeletal proof showing why π^e < e^π. 

2009—22nd Annual Field Day
Maximum number of pieces when cutting a pizza 6 times = 22. 

2008—21st Annual Field Day
Binet’s formula for Fibonacci numbers gives F₈ = 21. 

2005—19th Annual Field Day 
Front: a net for an icosahedron.

Back: an icosahedron and a formula for its volume. 

2005—19th Annual Field Day
 Front: a design illustrating that 19 is a hexagonal number. 

Back: a formula for H_n, the n^th hexagonal number, with H₂ = 19. 

2004—18th Annual Field Day
A Celtic knot with 18 crossings. 

2003—17th Annual Field Day
Gauss’ construction of a regular 17-gong. 

2002—16th Annual Field Day
A hypercube with its 16 vertices. 

2001—15th Annual Field Day
A combinatorial identity.