A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2905728 can be evenly divided by 1 2 3 4 6 7 8 12 14 16 21 23 24 28 32 42 46 47 48 56 64 69 84 92 94 96 112 128 138 141 161 168 184 188 192 224 276 282 322 329 336 368 376 384 448 483 552 564 644 658 672 736 752 896 966 987 1,081 1,104 1,128 1,288 1,316 1,344 1,472 1,504 1,932 1,974 2,162 2,208 2,256 2,576 2,632 2,688 2,944 3,008 3,243 3,864 3,948 4,324 4,416 4,512 5,152 5,264 6,016 6,486 7,567 7,728 7,896 8,648 8,832 9,024 10,304 10,528 12,972 15,134 15,456 15,792 17,296 18,048 20,608 21,056 22,701 25,944 30,268 30,912 31,584 34,592 42,112 45,402 51,888 60,536 61,824 63,168 69,184 90,804 103,776 121,072 126,336 138,368 181,608 207,552 242,144 363,216 415,104 484,288 726,432 968,576 1,452,864 and 2,905,728, with no remainder.
Since 2,905,728 cannot be divided by just 1 and 2,905,728, it is not a prime number.