theorem
  27 satisfies_Sierpinski_problem_87a
  proof
    reconsider a = 2 as Prime by XPRIMES1:2;
    reconsider b = 5 as Prime by XPRIMES1:5;
    reconsider c = 73 as Prime by XPRIMES1:73;
    take a,b,c;
    thus thesis by Th54;
  end;
