A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1816920 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 14 15 18 20 21 24 28 30 35 36 40 42 45 49 56 60 63 70 72 84 90 98 103 105 120 126 140 147 168 180 196 206 210 245 252 280 294 309 315 360 392 412 420 441 490 504 515 588 618 630 721 735 824 840 882 927 980 1,030 1,176 1,236 1,260 1,442 1,470 1,545 1,764 1,854 1,960 2,060 2,163 2,205 2,472 2,520 2,884 2,940 3,090 3,528 3,605 3,708 4,120 4,326 4,410 4,635 5,047 5,768 5,880 6,180 6,489 7,210 7,416 8,652 8,820 9,270 10,094 10,815 12,360 12,978 14,420 15,141 17,304 17,640 18,540 20,188 21,630 25,235 25,956 28,840 30,282 32,445 37,080 40,376 43,260 45,423 50,470 51,912 60,564 64,890 75,705 86,520 90,846 100,940 121,128 129,780 151,410 181,692 201,880 227,115 259,560 302,820 363,384 454,230 605,640 908,460 and 1,816,920, with no remainder.
Since 1,816,920 cannot be divided by just 1 and 1,816,920, it is not a prime number.