A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2857980 can be evenly divided by 1 2 3 4 5 6 10 12 15 19 20 23 30 38 46 57 60 69 76 92 95 109 114 115 138 190 218 228 230 276 285 327 345 380 436 437 460 545 570 654 690 874 1,090 1,140 1,308 1,311 1,380 1,635 1,748 2,071 2,180 2,185 2,507 2,622 3,270 4,142 4,370 5,014 5,244 6,213 6,540 6,555 7,521 8,284 8,740 10,028 10,355 12,426 12,535 13,110 15,042 20,710 24,852 25,070 26,220 30,084 31,065 37,605 41,420 47,633 50,140 62,130 75,210 95,266 124,260 142,899 150,420 190,532 238,165 285,798 476,330 571,596 714,495 952,660 1,428,990 and 2,857,980, with no remainder.
Since 2,857,980 cannot be divided by just 1 and 2,857,980, it is not a prime number.