A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 918000 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 16 17 18 20 24 25 27 30 34 36 40 45 48 50 51 54 60 68 72 75 80 85 90 100 102 108 120 125 135 136 144 150 153 170 180 200 204 216 225 240 250 255 270 272 300 306 340 360 375 400 408 425 432 450 459 500 510 540 600 612 675 680 720 750 765 816 850 900 918 1,000 1,020 1,080 1,125 1,200 1,224 1,275 1,350 1,360 1,500 1,530 1,700 1,800 1,836 2,000 2,040 2,125 2,160 2,250 2,295 2,448 2,550 2,700 3,000 3,060 3,375 3,400 3,600 3,672 3,825 4,080 4,250 4,500 4,590 5,100 5,400 6,000 6,120 6,375 6,750 6,800 7,344 7,650 8,500 9,000 9,180 10,200 10,800 11,475 12,240 12,750 13,500 15,300 17,000 18,000 18,360 19,125 20,400 22,950 25,500 27,000 30,600 34,000 36,720 38,250 45,900 51,000 54,000 57,375 61,200 76,500 91,800 102,000 114,750 153,000 183,600 229,500 306,000 459,000 and 918,000, with no remainder.
Since 918,000 cannot be divided by just 1 and 918,000, it is not a prime number.