reserve a,b,c,k,m,n for Nat;
reserve i,j for Integer;
reserve p for Prime;

theorem
  1 satisfies_Sierpinski_problem_121_for 5
  proof
    thus 5 * 2|^(2|^1) + 1 is composite by Lm2,XPRIMES0:21;
    thus thesis by NAT_1:14;
  end;
