A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1856232 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 18 21 24 28 29 36 42 56 58 63 72 84 87 116 126 127 168 174 203 232 252 254 261 348 381 406 504 508 522 609 696 762 812 889 1,016 1,044 1,143 1,218 1,524 1,624 1,778 1,827 2,088 2,286 2,436 2,667 3,048 3,556 3,654 3,683 4,572 4,872 5,334 7,112 7,308 7,366 8,001 9,144 10,668 11,049 14,616 14,732 16,002 21,336 22,098 25,781 29,464 32,004 33,147 44,196 51,562 64,008 66,294 77,343 88,392 103,124 132,588 154,686 206,248 232,029 265,176 309,372 464,058 618,744 928,116 and 1,856,232, with no remainder.
Since 1,856,232 cannot be divided by just 1 and 1,856,232, it is not a prime number.