A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 4084128 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 96 108 116 144 163 174 216 232 261 288 326 348 432 464 489 522 652 696 783 864 928 978 1,044 1,304 1,392 1,467 1,566 1,956 2,088 2,608 2,784 2,934 3,132 3,912 4,176 4,401 4,727 5,216 5,868 6,264 7,824 8,352 8,802 9,454 11,736 12,528 14,181 15,648 17,604 18,908 23,472 25,056 28,362 35,208 37,816 42,543 46,944 56,724 70,416 75,632 85,086 113,448 127,629 140,832 151,264 170,172 226,896 255,258 340,344 453,792 510,516 680,688 1,021,032 1,361,376 2,042,064 and 4,084,128, with no remainder.
Since 4,084,128 cannot be divided by just 1 and 4,084,128, it is not a prime number.