A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 7891680 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 20 24 30 32 40 41 48 60 80 82 96 120 123 160 164 205 240 246 328 401 410 480 492 615 656 802 820 984 1,203 1,230 1,312 1,604 1,640 1,968 2,005 2,406 2,460 3,208 3,280 3,936 4,010 4,812 4,920 6,015 6,416 6,560 8,020 9,624 9,840 12,030 12,832 16,040 16,441 19,248 19,680 24,060 32,080 32,882 38,496 48,120 49,323 64,160 65,764 82,205 96,240 98,646 131,528 164,410 192,480 197,292 246,615 263,056 328,820 394,584 493,230 526,112 657,640 789,168 986,460 1,315,280 1,578,336 1,972,920 2,630,560 3,945,840 and 7,891,680, with no remainder.
Since 7,891,680 cannot be divided by just 1 and 7,891,680, it is not a prime number.