A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2859948 can be evenly divided by 1 2 3 4 6 7 9 12 13 14 18 21 26 27 28 36 39 42 52 54 63 78 81 84 91 97 108 117 126 156 162 182 189 194 234 252 273 291 324 351 364 378 388 468 546 567 582 679 702 756 819 873 1,053 1,092 1,134 1,164 1,261 1,358 1,404 1,638 1,746 2,037 2,106 2,268 2,457 2,522 2,619 2,716 3,276 3,492 3,783 4,074 4,212 4,914 5,044 5,238 6,111 7,371 7,566 7,857 8,148 8,827 9,828 10,476 11,349 12,222 14,742 15,132 15,714 17,654 18,333 22,698 24,444 26,481 29,484 31,428 34,047 35,308 36,666 45,396 52,962 54,999 68,094 73,332 79,443 102,141 105,924 109,998 136,188 158,886 204,282 219,996 238,329 317,772 408,564 476,658 714,987 953,316 1,429,974 and 2,859,948, with no remainder.
Since 2,859,948 cannot be divided by just 1 and 2,859,948, it is not a prime number.