A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3185028 can be evenly divided by 1 2 3 4 6 7 9 11 12 14 18 21 22 27 28 33 36 42 44 54 63 66 77 84 99 108 126 132 154 189 198 231 252 297 308 378 383 396 462 594 693 756 766 924 1,149 1,188 1,386 1,532 2,079 2,298 2,681 2,772 3,447 4,158 4,213 4,596 5,362 6,894 8,043 8,316 8,426 10,341 10,724 12,639 13,788 16,086 16,852 20,682 24,129 25,278 29,491 32,172 37,917 41,364 48,258 50,556 58,982 72,387 75,834 88,473 96,516 113,751 117,964 144,774 151,668 176,946 227,502 265,419 289,548 353,892 455,004 530,838 796,257 1,061,676 1,592,514 and 3,185,028, with no remainder.
Since 3,185,028 cannot be divided by just 1 and 3,185,028, it is not a prime number.