A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2891928 can be evenly divided by 1 2 3 4 6 8 12 13 23 24 26 31 39 46 52 62 69 78 92 93 104 124 138 156 169 184 186 248 276 299 312 338 372 403 507 552 598 676 713 744 806 897 1,014 1,196 1,209 1,352 1,426 1,612 1,794 2,028 2,139 2,392 2,418 2,852 3,224 3,588 3,887 4,056 4,278 4,836 5,239 5,704 7,176 7,774 8,556 9,269 9,672 10,478 11,661 15,548 15,717 17,112 18,538 20,956 23,322 27,807 31,096 31,434 37,076 41,912 46,644 55,614 62,868 74,152 93,288 111,228 120,497 125,736 222,456 240,994 361,491 481,988 722,982 963,976 1,445,964 and 2,891,928, with no remainder.
Since 2,891,928 cannot be divided by just 1 and 2,891,928, it is not a prime number.