A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2831328 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 24 27 29 32 36 48 54 58 72 87 96 108 113 116 144 174 216 226 232 261 288 339 348 432 452 464 522 678 696 783 864 904 928 1,017 1,044 1,356 1,392 1,566 1,808 2,034 2,088 2,712 2,784 3,051 3,132 3,277 3,616 4,068 4,176 5,424 6,102 6,264 6,554 8,136 8,352 9,831 10,848 12,204 12,528 13,108 16,272 19,662 24,408 25,056 26,216 29,493 32,544 39,324 48,816 52,432 58,986 78,648 88,479 97,632 104,864 117,972 157,296 176,958 235,944 314,592 353,916 471,888 707,832 943,776 1,415,664 and 2,831,328, with no remainder.
Since 2,831,328 cannot be divided by just 1 and 2,831,328, it is not a prime number.