consider this way 1111(4 1's) divided by 270 Rem = 270 11111(5 1's) Rem = 0 111111(6 1's ) Rem= 1 (7 1's) Rem = 11 for 8 Rem = 111 for 9 Rem = 1111 for10Rem = 0 so similarly .... for 15 Rem = 0 for 20 Rem = 0 ..... for 1110 Rem =0 so by pattern for 1111 Rem =1 that is 1111......(1111 times) divided by 271 leaves 1 as remainder