A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 797580 can be evenly divided by 1 2 3 4 5 6 7 9 10 12 14 15 18 20 21 27 28 30 35 36 42 45 54 60 63 70 84 90 105 108 126 135 140 180 189 210 211 252 270 315 378 420 422 540 630 633 756 844 945 1,055 1,260 1,266 1,477 1,890 1,899 2,110 2,532 2,954 3,165 3,780 3,798 4,220 4,431 5,697 5,908 6,330 7,385 7,596 8,862 9,495 11,394 12,660 13,293 14,770 17,724 18,990 22,155 22,788 26,586 28,485 29,540 37,980 39,879 44,310 53,172 56,970 66,465 79,758 88,620 113,940 132,930 159,516 199,395 265,860 398,790 and 797,580, with no remainder.
Since 797,580 cannot be divided by just 1 and 797,580, it is not a prime number.