A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2860416 can be evenly divided by 1 2 3 4 6 8 9 12 13 16 18 24 26 32 36 39 48 52 64 72 78 96 104 117 128 144 156 191 192 208 234 288 312 382 384 416 468 573 576 624 764 832 936 1,146 1,152 1,248 1,528 1,664 1,719 1,872 2,292 2,483 2,496 3,056 3,438 3,744 4,584 4,966 4,992 6,112 6,876 7,449 7,488 9,168 9,932 12,224 13,752 14,898 14,976 18,336 19,864 22,347 24,448 27,504 29,796 36,672 39,728 44,694 55,008 59,592 73,344 79,456 89,388 110,016 119,184 158,912 178,776 220,032 238,368 317,824 357,552 476,736 715,104 953,472 1,430,208 and 2,860,416, with no remainder.
Since 2,860,416 cannot be divided by just 1 and 2,860,416, it is not a prime number.