A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1108536 can be evenly divided by 1 2 3 4 6 8 11 12 13 17 19 22 24 26 33 34 38 39 44 51 52 57 66 68 76 78 88 102 104 114 132 136 143 152 156 187 204 209 221 228 247 264 286 312 323 374 408 418 429 442 456 494 561 572 627 646 663 741 748 836 858 884 969 988 1,122 1,144 1,254 1,292 1,326 1,482 1,496 1,672 1,716 1,768 1,938 1,976 2,244 2,431 2,508 2,584 2,652 2,717 2,964 3,432 3,553 3,876 4,199 4,488 4,862 5,016 5,304 5,434 5,928 7,106 7,293 7,752 8,151 8,398 9,724 10,659 10,868 12,597 14,212 14,586 16,302 16,796 19,448 21,318 21,736 25,194 28,424 29,172 32,604 33,592 42,636 46,189 50,388 58,344 65,208 85,272 92,378 100,776 138,567 184,756 277,134 369,512 554,268 and 1,108,536, with no remainder.
Since 1,108,536 cannot be divided by just 1 and 1,108,536, it is not a prime number.