A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1153656 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 18 21 24 27 28 36 42 49 54 56 63 72 84 98 108 109 126 147 168 189 196 216 218 252 294 327 378 392 436 441 504 588 654 756 763 872 882 981 1,176 1,308 1,323 1,512 1,526 1,764 1,962 2,289 2,616 2,646 2,943 3,052 3,528 3,924 4,578 5,292 5,341 5,886 6,104 6,867 7,848 9,156 10,584 10,682 11,772 13,734 16,023 18,312 20,601 21,364 23,544 27,468 32,046 41,202 42,728 48,069 54,936 64,092 82,404 96,138 128,184 144,207 164,808 192,276 288,414 384,552 576,828 and 1,153,656, with no remainder.
Since 1,153,656 cannot be divided by just 1 and 1,153,656, it is not a prime number.