A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1861200 can be evenly divided by 1 2 3 4 5 6 8 9 10 11 12 15 16 18 20 22 24 25 30 33 36 40 44 45 47 48 50 55 60 66 72 75 80 88 90 94 99 100 110 120 132 141 144 150 165 176 180 188 198 200 220 225 235 240 264 275 282 300 330 360 376 396 400 423 440 450 470 495 517 528 550 564 600 660 705 720 752 792 825 846 880 900 940 990 1,034 1,100 1,128 1,175 1,200 1,320 1,410 1,551 1,584 1,650 1,692 1,800 1,880 1,980 2,068 2,115 2,200 2,256 2,350 2,475 2,585 2,640 2,820 3,102 3,300 3,384 3,525 3,600 3,760 3,960 4,136 4,230 4,400 4,653 4,700 4,950 5,170 5,640 6,204 6,600 6,768 7,050 7,755 7,920 8,272 8,460 9,306 9,400 9,900 10,340 10,575 11,280 12,408 12,925 13,200 14,100 15,510 16,920 18,612 18,800 19,800 20,680 21,150 23,265 24,816 25,850 28,200 31,020 33,840 37,224 38,775 39,600 41,360 42,300 46,530 51,700 56,400 62,040 74,448 77,550 84,600 93,060 103,400 116,325 124,080 155,100 169,200 186,120 206,800 232,650 310,200 372,240 465,300 620,400 930,600 and 1,861,200, with no remainder.
Since 1,861,200 cannot be divided by just 1 and 1,861,200, it is not a prime number.