A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1138320 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 16 17 18 20 24 27 30 31 34 36 40 45 48 51 54 60 62 68 72 80 85 90 93 102 108 120 124 135 136 144 153 155 170 180 186 204 216 240 248 255 270 272 279 306 310 340 360 372 408 432 459 465 496 510 527 540 558 612 620 680 720 744 765 816 837 918 930 1,020 1,054 1,080 1,116 1,224 1,240 1,360 1,395 1,488 1,530 1,581 1,674 1,836 1,860 2,040 2,108 2,160 2,232 2,295 2,448 2,480 2,635 2,790 3,060 3,162 3,348 3,672 3,720 4,080 4,185 4,216 4,464 4,590 4,743 5,270 5,580 6,120 6,324 6,696 7,344 7,440 7,905 8,370 8,432 9,180 9,486 10,540 11,160 12,240 12,648 13,392 14,229 15,810 16,740 18,360 18,972 21,080 22,320 23,715 25,296 28,458 31,620 33,480 36,720 37,944 42,160 47,430 56,916 63,240 66,960 71,145 75,888 94,860 113,832 126,480 142,290 189,720 227,664 284,580 379,440 569,160 and 1,138,320, with no remainder.
Since 1,138,320 cannot be divided by just 1 and 1,138,320, it is not a prime number.