A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1837920 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 16 20 21 24 28 30 32 35 40 42 48 56 60 70 80 84 96 105 112 120 140 160 168 210 224 240 280 336 420 480 547 560 672 840 1,094 1,120 1,641 1,680 2,188 2,735 3,282 3,360 3,829 4,376 5,470 6,564 7,658 8,205 8,752 10,940 11,487 13,128 15,316 16,410 17,504 19,145 21,880 22,974 26,256 30,632 32,820 38,290 43,760 45,948 52,512 57,435 61,264 65,640 76,580 87,520 91,896 114,870 122,528 131,280 153,160 183,792 229,740 262,560 306,320 367,584 459,480 612,640 918,960 and 1,837,920, with no remainder.
Since 1,837,920 cannot be divided by just 1 and 1,837,920, it is not a prime number.