Is Adobe Acrobat's icon a special function?
Solution 1:
The logo dates back to Adobe Reader v1.0. (link) I always thought it was chosen simply because it looks like the letter A for Acrobat.
A parametric function that approximates the logo is:
$$x(t)=5\cos(t)\times \left(\sin(t+.5)+\cos(3t+.5) \right) \\
y(t)=5\sin(t)\times \left(\sin(t+.5)-\cos(3t+.5) \right) $$
Solution 2:
It bears a strong resemblance to (in cartesian coordinates) $ x = \cos(t) + 3 \cos(2 t)/4, y = \sin(t) - 3 \sin(2 t)/4$ but not quite as symmetric.
