A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 819168 can be evenly divided by 1 2 3 4 6 7 8 12 14 16 21 23 24 28 32 42 46 48 53 56 69 84 92 96 106 112 138 159 161 168 184 212 224 276 318 322 336 368 371 424 483 552 636 644 672 736 742 848 966 1,104 1,113 1,219 1,272 1,288 1,484 1,696 1,932 2,208 2,226 2,438 2,544 2,576 2,968 3,657 3,864 4,452 4,876 5,088 5,152 5,936 7,314 7,728 8,533 8,904 9,752 11,872 14,628 15,456 17,066 17,808 19,504 25,599 29,256 34,132 35,616 39,008 51,198 58,512 68,264 102,396 117,024 136,528 204,792 273,056 409,584 and 819,168, with no remainder.
Since 819,168 cannot be divided by just 1 and 819,168, it is not a prime number.