A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2618550 can be evenly divided by 1 2 3 5 6 9 10 11 15 18 22 23 25 30 33 45 46 50 55 66 69 75 90 99 110 115 138 150 165 198 207 225 230 253 275 330 345 414 450 495 506 529 550 575 690 759 825 990 1,035 1,058 1,150 1,265 1,518 1,587 1,650 1,725 2,070 2,277 2,475 2,530 2,645 3,174 3,450 3,795 4,554 4,761 4,950 5,175 5,290 5,819 6,325 7,590 7,935 9,522 10,350 11,385 11,638 12,650 13,225 15,870 17,457 18,975 22,770 23,805 26,450 29,095 34,914 37,950 39,675 47,610 52,371 56,925 58,190 79,350 87,285 104,742 113,850 119,025 145,475 174,570 238,050 261,855 290,950 436,425 523,710 872,850 1,309,275 and 2,618,550, with no remainder.
Since 2,618,550 cannot be divided by just 1 and 2,618,550, it is not a prime number.