A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1838720 can be evenly divided by 1 2 4 5 8 10 13 16 17 20 26 32 34 40 52 64 65 68 80 85 104 128 130 136 160 169 170 208 221 260 272 320 338 340 416 442 520 544 640 676 680 832 845 884 1,040 1,088 1,105 1,352 1,360 1,664 1,690 1,768 2,080 2,176 2,210 2,704 2,720 2,873 3,380 3,536 4,160 4,420 5,408 5,440 5,746 6,760 7,072 8,320 8,840 10,816 10,880 11,492 13,520 14,144 14,365 17,680 21,632 22,984 27,040 28,288 28,730 35,360 45,968 54,080 57,460 70,720 91,936 108,160 114,920 141,440 183,872 229,840 367,744 459,680 919,360 and 1,838,720, with no remainder.
Since 1,838,720 cannot be divided by just 1 and 1,838,720, it is not a prime number.