A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1876392 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 17 18 21 24 27 28 34 36 42 51 54 56 63 68 72 73 84 102 108 119 126 136 146 153 168 189 204 216 219 238 252 292 306 357 378 408 438 459 476 504 511 584 612 657 714 756 876 918 952 1,022 1,071 1,224 1,241 1,314 1,428 1,512 1,533 1,752 1,836 1,971 2,044 2,142 2,482 2,628 2,856 3,066 3,213 3,672 3,723 3,942 4,088 4,284 4,599 4,964 5,256 6,132 6,426 7,446 7,884 8,568 8,687 9,198 9,928 11,169 12,264 12,852 13,797 14,892 15,768 17,374 18,396 22,338 25,704 26,061 27,594 29,784 33,507 34,748 36,792 44,676 52,122 55,188 67,014 69,496 78,183 89,352 104,244 110,376 134,028 156,366 208,488 234,549 268,056 312,732 469,098 625,464 938,196 and 1,876,392, with no remainder.
Since 1,876,392 cannot be divided by just 1 and 1,876,392, it is not a prime number.