A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 538020 can be evenly divided by 1 2 3 4 5 6 7 9 10 12 14 15 18 20 21 28 30 35 36 42 45 49 60 61 63 70 84 90 98 105 122 126 140 147 180 183 196 210 244 245 252 294 305 315 366 420 427 441 490 549 588 610 630 732 735 854 882 915 980 1,098 1,220 1,260 1,281 1,470 1,708 1,764 1,830 2,135 2,196 2,205 2,562 2,745 2,940 2,989 3,660 3,843 4,270 4,410 5,124 5,490 5,978 6,405 7,686 8,540 8,820 8,967 10,980 11,956 12,810 14,945 15,372 17,934 19,215 25,620 26,901 29,890 35,868 38,430 44,835 53,802 59,780 76,860 89,670 107,604 134,505 179,340 269,010 and 538,020, with no remainder.
Since 538,020 cannot be divided by just 1 and 538,020, it is not a prime number.