A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 852012 can be evenly divided by 1 2 3 4 6 7 9 12 14 18 21 23 27 28 36 42 46 49 54 63 69 84 92 98 108 126 138 147 161 189 196 207 252 276 294 322 343 378 414 441 483 588 621 644 686 756 828 882 966 1,029 1,127 1,242 1,323 1,372 1,449 1,764 1,932 2,058 2,254 2,484 2,646 2,898 3,087 3,381 4,116 4,347 4,508 5,292 5,796 6,174 6,762 7,889 8,694 9,261 10,143 12,348 13,524 15,778 17,388 18,522 20,286 23,667 30,429 31,556 37,044 40,572 47,334 60,858 71,001 94,668 121,716 142,002 213,003 284,004 426,006 and 852,012, with no remainder.
Since 852,012 cannot be divided by just 1 and 852,012, it is not a prime number.