A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2868390 can be evenly divided by 1 2 3 5 6 7 9 10 14 15 18 21 29 30 35 42 45 58 63 70 87 90 105 126 145 157 174 203 210 261 290 314 315 406 435 471 522 609 630 785 870 942 1,015 1,099 1,218 1,305 1,413 1,570 1,827 2,030 2,198 2,355 2,610 2,826 3,045 3,297 3,654 4,553 4,710 5,495 6,090 6,594 7,065 9,106 9,135 9,891 10,990 13,659 14,130 16,485 18,270 19,782 22,765 27,318 31,871 32,970 40,977 45,530 49,455 63,742 68,295 81,954 95,613 98,910 136,590 159,355 191,226 204,885 286,839 318,710 409,770 478,065 573,678 956,130 1,434,195 and 2,868,390, with no remainder.
Since 2,868,390 cannot be divided by just 1 and 2,868,390, it is not a prime number.