A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 5990166 can be evenly divided by 1 2 3 6 7 9 13 14 18 21 23 26 27 39 42 46 53 54 63 69 78 91 106 117 126 138 159 161 182 189 207 234 273 299 318 322 351 371 378 414 477 483 546 598 621 689 702 742 819 897 954 966 1,113 1,219 1,242 1,378 1,431 1,449 1,638 1,794 2,067 2,093 2,226 2,438 2,457 2,691 2,862 2,898 3,339 3,657 4,134 4,186 4,347 4,823 4,914 5,382 6,201 6,279 6,678 7,314 8,073 8,533 8,694 9,646 10,017 10,971 12,402 12,558 14,469 15,847 16,146 17,066 18,603 18,837 20,034 21,942 25,599 28,938 31,694 32,913 37,206 37,674 43,407 47,541 51,198 56,511 65,826 76,797 86,814 95,082 110,929 113,022 130,221 142,623 153,594 221,858 230,391 260,442 285,246 332,787 427,869 460,782 665,574 855,738 998,361 1,996,722 2,995,083 and 5,990,166, with no remainder.
Since 5,990,166 cannot be divided by just 1 and 5,990,166, it is not a prime number.