A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1901900 can be evenly divided by 1 2 4 5 7 10 11 13 14 19 20 22 25 26 28 35 38 44 50 52 55 65 70 76 77 91 95 100 110 130 133 140 143 154 175 182 190 209 220 247 260 266 275 286 308 325 350 364 380 385 418 455 475 494 532 550 572 650 665 700 715 770 836 910 950 988 1,001 1,045 1,100 1,235 1,300 1,330 1,430 1,463 1,540 1,729 1,820 1,900 1,925 2,002 2,090 2,275 2,470 2,660 2,717 2,860 2,926 3,325 3,458 3,575 3,850 4,004 4,180 4,550 4,940 5,005 5,225 5,434 5,852 6,175 6,650 6,916 7,150 7,315 7,700 8,645 9,100 10,010 10,450 10,868 12,350 13,300 13,585 14,300 14,630 17,290 19,019 20,020 20,900 24,700 25,025 27,170 29,260 34,580 36,575 38,038 43,225 50,050 54,340 67,925 73,150 76,076 86,450 95,095 100,100 135,850 146,300 172,900 190,190 271,700 380,380 475,475 950,950 and 1,901,900, with no remainder.
Since 1,901,900 cannot be divided by just 1 and 1,901,900, it is not a prime number.