Write the letters of the alphabet around a circle, then strike out the letters that are symmetrical about a vertical line. The remaining letters are grouped in clumps of 3, 1, 4, 1, and 6 letters.
I’ve heard that this observation is due to Martin Gardner, but I don’t have a specific reference.
In case you’re interested, here’s the Python script I wrote to make the image above.
from numpy import *
import matplotlib.pyplot as plt
for i in range(26):
letter = chr(ord('A') + i)
if letter in "AHIMOTUVWXY":
latex = r"$\equiv\!\!\!\!\!" + letter + "$"
else:
latex = f"${letter}$"
theta = pi/2 - 2*pi*i/26
pt = (0.5*cos(theta), 0.5*sin(theta))
plt.plot(pt[0], pt[1], ' ')
plt.annotate(latex, pt, fontsize="xx-large")
plt.axis("off")
plt.gca().set_aspect("equal")
plt.savefig("alphabet_pi.png")