A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1842120 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 14 15 17 18 20 21 24 28 30 34 35 36 40 42 43 45 51 56 60 63 68 70 72 84 85 86 90 102 105 119 120 126 129 136 140 153 168 170 172 180 204 210 215 238 252 255 258 280 301 306 315 340 344 357 360 387 408 420 430 476 504 510 516 595 602 612 630 645 680 714 731 765 774 840 860 903 952 1,020 1,032 1,071 1,190 1,204 1,224 1,260 1,290 1,428 1,462 1,505 1,530 1,548 1,720 1,785 1,806 1,935 2,040 2,142 2,193 2,380 2,408 2,520 2,580 2,709 2,856 2,924 3,010 3,060 3,096 3,570 3,612 3,655 3,870 4,284 4,386 4,515 4,760 5,117 5,160 5,355 5,418 5,848 6,020 6,120 6,579 7,140 7,224 7,310 7,740 8,568 8,772 9,030 10,234 10,710 10,836 10,965 12,040 13,158 13,545 14,280 14,620 15,351 15,480 17,544 18,060 20,468 21,420 21,672 21,930 25,585 26,316 27,090 29,240 30,702 32,895 36,120 40,936 42,840 43,860 46,053 51,170 52,632 54,180 61,404 65,790 76,755 87,720 92,106 102,340 108,360 122,808 131,580 153,510 184,212 204,680 230,265 263,160 307,020 368,424 460,530 614,040 921,060 and 1,842,120, with no remainder.
Since 1,842,120 cannot be divided by just 1 and 1,842,120, it is not a prime number.