A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6428268 can be evenly divided by 1 2 3 4 6 7 9 11 12 14 18 21 22 27 28 33 36 42 44 54 63 66 77 84 99 108 126 132 154 189 198 231 252 297 308 378 396 462 594 693 756 773 924 1,188 1,386 1,546 2,079 2,319 2,772 3,092 4,158 4,638 5,411 6,957 8,316 8,503 9,276 10,822 13,914 16,233 17,006 20,871 21,644 25,509 27,828 32,466 34,012 41,742 48,699 51,018 59,521 64,932 76,527 83,484 97,398 102,036 119,042 146,097 153,054 178,563 194,796 229,581 238,084 292,194 306,108 357,126 459,162 535,689 584,388 714,252 918,324 1,071,378 1,607,067 2,142,756 3,214,134 and 6,428,268, with no remainder.
Since 6,428,268 cannot be divided by just 1 and 6,428,268, it is not a prime number.