
theorem
  911 is prime
proof
  now
    911 = 2*455 + 1; hence not 2 divides 911 by NAT_4:9;
    911 = 3*303 + 2; hence not 3 divides 911 by NAT_4:9;
    911 = 5*182 + 1; hence not 5 divides 911 by NAT_4:9;
    911 = 7*130 + 1; hence not 7 divides 911 by NAT_4:9;
    911 = 11*82 + 9; hence not 11 divides 911 by NAT_4:9;
    911 = 13*70 + 1; hence not 13 divides 911 by NAT_4:9;
    911 = 17*53 + 10; hence not 17 divides 911 by NAT_4:9;
    911 = 19*47 + 18; hence not 19 divides 911 by NAT_4:9;
    911 = 23*39 + 14; hence not 23 divides 911 by NAT_4:9;
    911 = 29*31 + 12; hence not 29 divides 911 by NAT_4:9;
  end;
  then for n being Element of NAT st 1 < n & n*n <= 911 & n is prime
  holds not n divides 911 by XPRIMET1:20;
  hence thesis by NAT_4:14;
end;
