1. 20
  1.  

  2. 4

    Neat! I clicked through to the Trinity Hall prime that inspired the Corpus Christi prime, and was surprised to find that the former prime was obtained with a very different technique:

    Professor McKee explains: “Most of the digits of p were fixed so that: (i) the top two thirds made the desired pattern; (ii) the bottom third ensured that p-1 had a nice large (composite) factor F with the factorisation of F known. Numbers of this shape can easily be checked for primality. A small number of digits (you can see which!) were looped over until p was found that was prime.”