A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2505510 can be evenly divided by 1 2 3 5 6 7 9 10 14 15 18 21 30 35 41 42 45 63 70 82 90 97 105 123 126 194 205 210 246 287 291 315 369 410 485 574 582 615 630 679 738 861 873 970 1,230 1,358 1,435 1,455 1,722 1,746 1,845 2,037 2,583 2,870 2,910 3,395 3,690 3,977 4,074 4,305 4,365 5,166 6,111 6,790 7,954 8,610 8,730 10,185 11,931 12,222 12,915 19,885 20,370 23,862 25,830 27,839 30,555 35,793 39,770 55,678 59,655 61,110 71,586 83,517 119,310 139,195 167,034 178,965 250,551 278,390 357,930 417,585 501,102 835,170 1,252,755 and 2,505,510, with no remainder.
Since 2,505,510 cannot be divided by just 1 and 2,505,510, it is not a prime number.