Problem 3a.

command triangle a b c
{
   repeat e 0 c
   {
      pen (c/2-e)
      smaller? (c/2) e
      {
         pen (e-c/2)
      }
      line (a+e) b (a+c/3) (b+2*c/5)
   }
}
paper 17
repeat k 13 1

{
   triangle (2*k) (k*k*k/90) (k*k)
}

-gary escudero