A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2158650 can be evenly divided by 1 2 3 5 6 9 10 13 15 18 25 26 27 30 39 41 45 50 54 65 75 78 81 82 90 117 123 130 135 150 162 195 205 225 234 246 270 325 351 369 390 405 410 450 533 585 615 650 675 702 738 810 975 1,025 1,053 1,066 1,107 1,170 1,230 1,350 1,599 1,755 1,845 1,950 2,025 2,050 2,106 2,214 2,665 2,925 3,075 3,198 3,321 3,510 3,690 4,050 4,797 5,265 5,330 5,535 5,850 6,150 6,642 7,995 8,775 9,225 9,594 10,530 11,070 13,325 14,391 15,990 16,605 17,550 18,450 23,985 26,325 26,650 27,675 28,782 33,210 39,975 43,173 47,970 52,650 55,350 71,955 79,950 83,025 86,346 119,925 143,910 166,050 215,865 239,850 359,775 431,730 719,550 1,079,325 and 2,158,650, with no remainder.
Since 2,158,650 cannot be divided by just 1 and 2,158,650, it is not a prime number.