A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2346408 can be evenly divided by 1 2 3 4 6 8 9 12 17 18 24 27 34 36 51 54 68 71 72 81 102 108 136 142 153 162 204 213 216 243 284 306 324 408 426 459 486 568 612 639 648 852 918 972 1,207 1,224 1,278 1,377 1,704 1,836 1,917 1,944 2,414 2,556 2,754 3,621 3,672 3,834 4,131 4,828 5,112 5,508 5,751 7,242 7,668 8,262 9,656 10,863 11,016 11,502 14,484 15,336 16,524 17,253 21,726 23,004 28,968 32,589 33,048 34,506 43,452 46,008 65,178 69,012 86,904 97,767 130,356 138,024 195,534 260,712 293,301 391,068 586,602 782,136 1,173,204 and 2,346,408, with no remainder.
Since 2,346,408 cannot be divided by just 1 and 2,346,408, it is not a prime number.