A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 798600 can be evenly divided by 1 2 3 4 5 6 8 10 11 12 15 20 22 24 25 30 33 40 44 50 55 60 66 75 88 100 110 120 121 132 150 165 200 220 242 264 275 300 330 363 440 484 550 600 605 660 726 825 968 1,100 1,210 1,320 1,331 1,452 1,650 1,815 2,200 2,420 2,662 2,904 3,025 3,300 3,630 3,993 4,840 5,324 6,050 6,600 6,655 7,260 7,986 9,075 10,648 12,100 13,310 14,520 15,972 18,150 19,965 24,200 26,620 31,944 33,275 36,300 39,930 53,240 66,550 72,600 79,860 99,825 133,100 159,720 199,650 266,200 399,300 and 798,600, with no remainder.
Since 798,600 cannot be divided by just 1 and 798,600, it is not a prime number.