A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 585000 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 13 15 18 20 24 25 26 30 36 39 40 45 50 52 60 65 72 75 78 90 100 104 117 120 125 130 150 156 180 195 200 225 234 250 260 300 312 325 360 375 390 450 468 500 520 585 600 625 650 750 780 900 936 975 1,000 1,125 1,170 1,250 1,300 1,500 1,560 1,625 1,800 1,875 1,950 2,250 2,340 2,500 2,600 2,925 3,000 3,250 3,750 3,900 4,500 4,680 4,875 5,000 5,625 5,850 6,500 7,500 7,800 8,125 9,000 9,750 11,250 11,700 13,000 14,625 15,000 16,250 19,500 22,500 23,400 24,375 29,250 32,500 39,000 45,000 48,750 58,500 65,000 73,125 97,500 117,000 146,250 195,000 292,500 and 585,000, with no remainder.
Since 585,000 cannot be divided by just 1 and 585,000, it is not a prime number.