A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2142816 can be evenly divided by 1 2 3 4 6 8 12 13 16 17 24 26 32 34 39 48 51 52 68 78 96 101 102 104 136 156 202 204 208 221 272 303 312 404 408 416 442 544 606 624 663 808 816 884 1,212 1,248 1,313 1,326 1,616 1,632 1,717 1,768 2,424 2,626 2,652 3,232 3,434 3,536 3,939 4,848 5,151 5,252 5,304 6,868 7,072 7,878 9,696 10,302 10,504 10,608 13,736 15,756 20,604 21,008 21,216 22,321 27,472 31,512 41,208 42,016 44,642 54,944 63,024 66,963 82,416 89,284 126,048 133,926 164,832 178,568 267,852 357,136 535,704 714,272 1,071,408 and 2,142,816, with no remainder.
Since 2,142,816 cannot be divided by just 1 and 2,142,816, it is not a prime number.