
theorem
  241 is prime
proof
  now
    241 = 2*120 + 1; hence not 2 divides 241 by NAT_4:9;
    241 = 3*80 + 1; hence not 3 divides 241 by NAT_4:9;
    241 = 5*48 + 1; hence not 5 divides 241 by NAT_4:9;
    241 = 7*34 + 3; hence not 7 divides 241 by NAT_4:9;
    241 = 11*21 + 10; hence not 11 divides 241 by NAT_4:9;
    241 = 13*18 + 7; hence not 13 divides 241 by NAT_4:9;
  end;
  then for n being Element of NAT st 1 < n & n*n <= 241 & n is prime
  holds not n divides 241 by XPRIMET1:12;
  hence thesis by NAT_4:14;
end;
