A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6888672 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 17 18 21 24 27 28 32 34 36 42 48 51 54 56 63 67 68 72 84 96 102 108 112 119 126 134 136 144 153 168 189 201 204 216 224 238 252 268 272 288 306 336 357 378 402 408 432 459 469 476 504 536 544 603 612 672 714 756 804 816 864 918 938 952 1,008 1,071 1,072 1,139 1,206 1,224 1,407 1,428 1,512 1,608 1,632 1,809 1,836 1,876 1,904 2,016 2,142 2,144 2,278 2,412 2,448 2,814 2,856 3,024 3,213 3,216 3,417 3,618 3,672 3,752 3,808 4,221 4,284 4,556 4,824 4,896 5,628 5,712 6,048 6,426 6,432 6,834 7,236 7,344 7,504 7,973 8,442 8,568 9,112 9,648 10,251 11,256 11,424 12,663 12,852 13,668 14,472 14,688 15,008 15,946 16,884 17,136 18,224 19,296 20,502 22,512 23,919 25,326 25,704 27,336 28,944 30,753 31,892 33,768 34,272 36,448 41,004 45,024 47,838 50,652 51,408 54,672 57,888 61,506 63,784 67,536 71,757 82,008 95,676 101,304 102,816 109,344 123,012 127,568 135,072 143,514 164,016 191,352 202,608 215,271 246,024 255,136 287,028 328,032 382,704 405,216 430,542 492,048 574,056 765,408 861,084 984,096 1,148,112 1,722,168 2,296,224 3,444,336 and 6,888,672, with no remainder.
Since 6,888,672 cannot be divided by just 1 and 6,888,672, it is not a prime number.