A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6408072 can be evenly divided by 1 2 3 4 6 8 9 11 12 18 22 24 27 29 31 33 36 44 54 58 62 66 72 81 87 88 93 99 108 116 124 132 162 174 186 198 216 232 248 261 264 279 297 319 324 341 348 372 396 522 558 594 638 648 682 696 744 783 792 837 891 899 957 1,023 1,044 1,116 1,188 1,276 1,364 1,566 1,674 1,782 1,798 1,914 2,046 2,088 2,232 2,349 2,376 2,511 2,552 2,697 2,728 2,871 3,069 3,132 3,348 3,564 3,596 3,828 4,092 4,698 5,022 5,394 5,742 6,138 6,264 6,696 7,128 7,192 7,656 8,091 8,184 8,613 9,207 9,396 9,889 10,044 10,788 11,484 12,276 16,182 17,226 18,414 18,792 19,778 20,088 21,576 22,968 24,273 24,552 25,839 27,621 29,667 32,364 34,452 36,828 39,556 48,546 51,678 55,242 59,334 64,728 68,904 72,819 73,656 79,112 89,001 97,092 103,356 110,484 118,668 145,638 178,002 194,184 206,712 220,968 237,336 267,003 291,276 356,004 534,006 582,552 712,008 801,009 1,068,012 1,602,018 2,136,024 3,204,036 and 6,408,072, with no remainder.
Since 6,408,072 cannot be divided by just 1 and 6,408,072, it is not a prime number.