A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 7881048 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 18 19 21 24 28 36 38 42 56 57 63 72 76 84 114 126 133 152 168 171 228 252 266 342 399 456 504 532 684 798 823 1,064 1,197 1,368 1,596 1,646 2,394 2,469 3,192 3,292 4,788 4,938 5,761 6,584 7,407 9,576 9,876 11,522 14,814 15,637 17,283 19,752 23,044 29,628 31,274 34,566 46,088 46,911 51,849 59,256 62,548 69,132 93,822 103,698 109,459 125,096 138,264 140,733 187,644 207,396 218,918 281,466 328,377 375,288 414,792 437,836 562,932 656,754 875,672 985,131 1,125,864 1,313,508 1,970,262 2,627,016 3,940,524 and 7,881,048, with no remainder.
Since 7,881,048 cannot be divided by just 1 and 7,881,048, it is not a prime number.