A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2186352 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 27 28 36 42 48 54 56 63 72 81 84 108 112 126 144 162 168 189 216 241 252 324 336 378 432 482 504 567 648 723 756 964 1,008 1,134 1,296 1,446 1,512 1,687 1,928 2,169 2,268 2,892 3,024 3,374 3,856 4,338 4,536 5,061 5,784 6,507 6,748 8,676 9,072 10,122 11,568 13,014 13,496 15,183 17,352 19,521 20,244 26,028 26,992 30,366 34,704 39,042 40,488 45,549 52,056 60,732 78,084 80,976 91,098 104,112 121,464 136,647 156,168 182,196 242,928 273,294 312,336 364,392 546,588 728,784 1,093,176 and 2,186,352, with no remainder.
Since 2,186,352 cannot be divided by just 1 and 2,186,352, it is not a prime number.