A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8420112 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 24 27 36 48 54 72 73 81 89 108 144 146 162 178 216 219 267 292 324 356 432 438 534 584 648 657 712 801 876 1,068 1,168 1,296 1,314 1,424 1,602 1,752 1,971 2,136 2,403 2,628 3,204 3,504 3,942 4,272 4,806 5,256 5,913 6,408 6,497 7,209 7,884 9,612 10,512 11,826 12,816 12,994 14,418 15,768 19,224 19,491 23,652 25,988 28,836 31,536 38,448 38,982 47,304 51,976 57,672 58,473 77,964 94,608 103,952 115,344 116,946 155,928 175,419 233,892 311,856 350,838 467,784 526,257 701,676 935,568 1,052,514 1,403,352 2,105,028 2,806,704 4,210,056 and 8,420,112, with no remainder.
Since 8,420,112 cannot be divided by just 1 and 8,420,112, it is not a prime number.