A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 876000 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 20 24 25 30 32 40 48 50 60 73 75 80 96 100 120 125 146 150 160 200 219 240 250 292 300 365 375 400 438 480 500 584 600 730 750 800 876 1,000 1,095 1,168 1,200 1,460 1,500 1,752 1,825 2,000 2,190 2,336 2,400 2,920 3,000 3,504 3,650 4,000 4,380 5,475 5,840 6,000 7,008 7,300 8,760 9,125 10,950 11,680 12,000 14,600 17,520 18,250 21,900 27,375 29,200 35,040 36,500 43,800 54,750 58,400 73,000 87,600 109,500 146,000 175,200 219,000 292,000 438,000 and 876,000, with no remainder.
Since 876,000 cannot be divided by just 1 and 876,000, it is not a prime number.