A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1546116 can be evenly divided by 1 2 3 4 6 11 12 13 17 22 26 33 34 39 44 51 52 53 66 68 78 102 106 132 143 156 159 187 204 212 221 286 318 374 429 442 561 572 583 636 663 689 748 858 884 901 1,122 1,166 1,326 1,378 1,716 1,749 1,802 2,067 2,244 2,332 2,431 2,652 2,703 2,756 3,498 3,604 4,134 4,862 5,406 6,996 7,293 7,579 8,268 9,724 9,911 10,812 11,713 14,586 15,158 19,822 22,737 23,426 29,172 29,733 30,316 35,139 39,644 45,474 46,852 59,466 70,278 90,948 118,932 128,843 140,556 257,686 386,529 515,372 773,058 and 1,546,116, with no remainder.
Since 1,546,116 cannot be divided by just 1 and 1,546,116, it is not a prime number.