A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 518700 can be evenly divided by 1 2 3 4 5 6 7 10 12 13 14 15 19 20 21 25 26 28 30 35 38 39 42 50 52 57 60 65 70 75 76 78 84 91 95 100 105 114 130 133 140 150 156 175 182 190 195 210 228 247 260 266 273 285 300 325 350 364 380 390 399 420 455 475 494 525 532 546 570 650 665 700 741 780 798 910 950 975 988 1,050 1,092 1,140 1,235 1,300 1,330 1,365 1,425 1,482 1,596 1,729 1,820 1,900 1,950 1,995 2,100 2,275 2,470 2,660 2,730 2,850 2,964 3,325 3,458 3,705 3,900 3,990 4,550 4,940 5,187 5,460 5,700 6,175 6,650 6,825 6,916 7,410 7,980 8,645 9,100 9,975 10,374 12,350 13,300 13,650 14,820 17,290 18,525 19,950 20,748 24,700 25,935 27,300 34,580 37,050 39,900 43,225 51,870 74,100 86,450 103,740 129,675 172,900 259,350 and 518,700, with no remainder.
Since 518,700 cannot be divided by just 1 and 518,700, it is not a prime number.