A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2599350 can be evenly divided by 1 2 3 5 6 10 13 15 25 26 30 31 39 43 50 62 65 75 78 86 93 129 130 150 155 186 195 215 258 310 325 390 403 430 465 559 645 650 775 806 930 975 1,075 1,118 1,209 1,290 1,333 1,550 1,677 1,950 2,015 2,150 2,325 2,418 2,666 2,795 3,225 3,354 3,999 4,030 4,650 5,590 6,045 6,450 6,665 7,998 8,385 10,075 12,090 13,330 13,975 16,770 17,329 19,995 20,150 27,950 30,225 33,325 34,658 39,990 41,925 51,987 60,450 66,650 83,850 86,645 99,975 103,974 173,290 199,950 259,935 433,225 519,870 866,450 1,299,675 and 2,599,350, with no remainder.
Since 2,599,350 cannot be divided by just 1 and 2,599,350, it is not a prime number.