A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 827904 can be evenly divided by 1 2 3 4 6 7 8 11 12 14 16 21 22 24 28 32 33 42 44 48 49 56 64 66 77 84 88 96 98 112 128 132 147 154 168 176 192 196 224 231 256 264 294 308 336 352 384 392 448 462 512 528 539 588 616 672 704 768 784 896 924 1,056 1,078 1,176 1,232 1,344 1,408 1,536 1,568 1,617 1,792 1,848 2,112 2,156 2,352 2,464 2,688 2,816 3,136 3,234 3,584 3,696 4,224 4,312 4,704 4,928 5,376 5,632 6,272 6,468 7,392 8,448 8,624 9,408 9,856 10,752 12,544 12,936 14,784 16,896 17,248 18,816 19,712 25,088 25,872 29,568 34,496 37,632 39,424 51,744 59,136 68,992 75,264 103,488 118,272 137,984 206,976 275,968 413,952 and 827,904, with no remainder.
Since 827,904 cannot be divided by just 1 and 827,904, it is not a prime number.