A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2988648 can be evenly divided by 1 2 3 4 6 8 9 12 13 18 24 26 31 36 39 52 62 72 78 93 103 104 117 124 156 186 206 234 248 279 309 312 372 403 412 468 558 618 744 806 824 927 936 1,116 1,209 1,236 1,339 1,612 1,854 2,232 2,418 2,472 2,678 3,193 3,224 3,627 3,708 4,017 4,836 5,356 6,386 7,254 7,416 8,034 9,579 9,672 10,712 12,051 12,772 14,508 16,068 19,158 24,102 25,544 28,737 29,016 32,136 38,316 41,509 48,204 57,474 76,632 83,018 96,408 114,948 124,527 166,036 229,896 249,054 332,072 373,581 498,108 747,162 996,216 1,494,324 and 2,988,648, with no remainder.
Since 2,988,648 cannot be divided by just 1 and 2,988,648, it is not a prime number.