A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1223040 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 13 14 15 16 20 21 24 26 28 30 32 35 39 40 42 48 49 52 56 60 64 65 70 78 80 84 91 96 98 104 105 112 120 128 130 140 147 156 160 168 182 192 195 196 208 210 224 240 245 260 273 280 294 312 320 336 364 384 390 392 416 420 448 455 480 490 520 546 560 588 624 637 640 672 728 735 780 784 832 840 896 910 960 980 1,040 1,092 1,120 1,176 1,248 1,274 1,344 1,365 1,456 1,470 1,560 1,568 1,664 1,680 1,820 1,911 1,920 1,960 2,080 2,184 2,240 2,352 2,496 2,548 2,688 2,730 2,912 2,940 3,120 3,136 3,185 3,360 3,640 3,822 3,920 4,160 4,368 4,480 4,704 4,992 5,096 5,460 5,824 5,880 6,240 6,272 6,370 6,720 7,280 7,644 7,840 8,320 8,736 9,408 9,555 10,192 10,920 11,648 11,760 12,480 12,740 13,440 14,560 15,288 15,680 17,472 18,816 19,110 20,384 21,840 23,520 24,960 25,480 29,120 30,576 31,360 34,944 38,220 40,768 43,680 47,040 50,960 58,240 61,152 76,440 81,536 87,360 94,080 101,920 122,304 152,880 174,720 203,840 244,608 305,760 407,680 611,520 and 1,223,040, with no remainder.
Since 1,223,040 cannot be divided by just 1 and 1,223,040, it is not a prime number.