A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2658096 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 27 28 36 42 48 54 56 63 72 81 84 108 112 126 144 162 168 189 216 252 293 324 336 378 432 504 567 586 648 756 879 1,008 1,134 1,172 1,296 1,512 1,758 2,051 2,268 2,344 2,637 3,024 3,516 4,102 4,536 4,688 5,274 6,153 7,032 7,911 8,204 9,072 10,548 12,306 14,064 15,822 16,408 18,459 21,096 23,733 24,612 31,644 32,816 36,918 42,192 47,466 49,224 55,377 63,288 73,836 94,932 98,448 110,754 126,576 147,672 166,131 189,864 221,508 295,344 332,262 379,728 443,016 664,524 886,032 1,329,048 and 2,658,096, with no remainder.
Since 2,658,096 cannot be divided by just 1 and 2,658,096, it is not a prime number.