6661 = (2 * 3330) + 1 ;
hence not 2 divides 6661 by NAT_4:9; :: thesis:
6661 = (3 * 2220) + 1 ;
hence not 3 divides 6661 by NAT_4:9; :: thesis:
6661 = (5 * 1332) + 1 ;
hence not 5 divides 6661 by NAT_4:9; :: thesis:
6661 = (7 * 951) + 4 ;
hence not 7 divides 6661 by NAT_4:9; :: thesis:
6661 = (11 * 605) + 6 ;
hence not 11 divides 6661 by NAT_4:9; :: thesis:
6661 = (13 * 512) + 5 ;
hence not 13 divides 6661 by NAT_4:9; :: thesis:
6661 = (17 * 391) + 14 ;
hence not 17 divides 6661 by NAT_4:9; :: thesis:
6661 = (19 * 350) + 11 ;
hence not 19 divides 6661 by NAT_4:9; :: thesis:
6661 = (23 * 289) + 14 ;
hence not 23 divides 6661 by NAT_4:9; :: thesis:
6661 = (29 * 229) + 20 ;
hence not 29 divides 6661 by NAT_4:9; :: thesis:
6661 = (31 * 214) + 27 ;
hence not 31 divides 6661 by NAT_4:9; :: thesis:
6661 = (37 * 180) + 1 ;
hence not 37 divides 6661 by NAT_4:9; :: thesis:
6661 = (41 * 162) + 19 ;
hence not 41 divides 6661 by NAT_4:9; :: thesis:
6661 = (43 * 154) + 39 ;
hence not 43 divides 6661 by NAT_4:9; :: thesis:
6661 = (47 * 141) + 34 ;
hence not 47 divides 6661 by NAT_4:9; :: thesis:
6661 = (53 * 125) + 36 ;
hence not 53 divides 6661 by NAT_4:9; :: thesis:
6661 = (59 * 112) + 53 ;
hence not 59 divides 6661 by NAT_4:9; :: thesis:
6661 = (61 * 109) + 12 ;
hence not 61 divides 6661 by NAT_4:9; :: thesis:
6661 = (67 * 99) + 28 ;
hence not 67 divides 6661 by NAT_4:9; :: thesis:
6661 = (71 * 93) + 58 ;
hence not 71 divides 6661 by NAT_4:9; :: thesis:
6661 = (73 * 91) + 18 ;
hence not 73 divides 6661 by NAT_4:9; :: thesis:
6661 = (79 * 84) + 25 ;
hence not 79 divides 6661 by NAT_4:9; :: thesis:

end;

then for n being Element of NAT st 1 < n & n * n <= 6661 & n is prime holds
not n divides 6661 by XPRIMET1:44;
hence 6661 is prime by NAT_4:14; :: thesis: