A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1658340 can be evenly divided by 1 2 3 4 5 6 9 10 12 15 18 20 27 30 36 37 45 54 60 74 83 90 108 111 135 148 166 180 185 222 249 270 332 333 370 415 444 498 540 555 666 740 747 830 996 999 1,110 1,245 1,332 1,494 1,660 1,665 1,998 2,220 2,241 2,490 2,988 3,071 3,330 3,735 3,996 4,482 4,980 4,995 6,142 6,660 7,470 8,964 9,213 9,990 11,205 12,284 14,940 15,355 18,426 19,980 22,410 27,639 30,710 36,852 44,820 46,065 55,278 61,420 82,917 92,130 110,556 138,195 165,834 184,260 276,390 331,668 414,585 552,780 829,170 and 1,658,340, with no remainder.
Since 1,658,340 cannot be divided by just 1 and 1,658,340, it is not a prime number.