A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1161440 can be evenly divided by 1 2 4 5 7 8 10 14 16 17 20 28 32 34 35 40 56 61 68 70 80 85 112 119 122 136 140 160 170 224 238 244 272 280 305 340 427 476 488 544 560 595 610 680 854 952 976 1,037 1,120 1,190 1,220 1,360 1,708 1,904 1,952 2,074 2,135 2,380 2,440 2,720 3,416 3,808 4,148 4,270 4,760 4,880 5,185 6,832 7,259 8,296 8,540 9,520 9,760 10,370 13,664 14,518 16,592 17,080 19,040 20,740 29,036 33,184 34,160 36,295 41,480 58,072 68,320 72,590 82,960 116,144 145,180 165,920 232,288 290,360 580,720 and 1,161,440, with no remainder.
Since 1,161,440 cannot be divided by just 1 and 1,161,440, it is not a prime number.