Here is a zoom out by a factor of two from yesterday’s picture. The triangular shape at the top is called a Tricorn or Mandelbar. The parameter a is 2.5. (See Bugs #8 for a description of the formula.) The image is centered at .
The Tricorn set is generated by . The standard formula is modified to use the complex conjugate of z. Here is a non-paywall academic paper on Tricorns