A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1785000 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 17 20 21 24 25 28 30 34 35 40 42 50 51 56 60 68 70 75 84 85 100 102 105 119 120 125 136 140 150 168 170 175 200 204 210 238 250 255 280 300 340 350 357 375 408 420 425 476 500 510 525 595 600 625 680 700 714 750 840 850 875 952 1,000 1,020 1,050 1,190 1,250 1,275 1,400 1,428 1,500 1,700 1,750 1,785 1,875 2,040 2,100 2,125 2,380 2,500 2,550 2,625 2,856 2,975 3,000 3,400 3,500 3,570 3,750 4,200 4,250 4,375 4,760 5,000 5,100 5,250 5,950 6,375 7,000 7,140 7,500 8,500 8,750 8,925 10,200 10,500 10,625 11,900 12,750 13,125 14,280 14,875 15,000 17,000 17,500 17,850 21,000 21,250 23,800 25,500 26,250 29,750 31,875 35,000 35,700 42,500 44,625 51,000 52,500 59,500 63,750 71,400 74,375 85,000 89,250 105,000 119,000 127,500 148,750 178,500 223,125 255,000 297,500 357,000 446,250 595,000 892,500 and 1,785,000, with no remainder.
Since 1,785,000 cannot be divided by just 1 and 1,785,000, it is not a prime number.