A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2911788 can be evenly divided by 1 2 3 4 6 9 11 12 18 19 22 27 33 36 38 43 44 54 57 66 76 81 86 99 108 114 129 132 162 171 172 198 209 228 258 297 324 342 387 396 418 473 513 516 594 627 684 774 817 836 891 946 1,026 1,161 1,188 1,254 1,419 1,539 1,548 1,634 1,782 1,881 1,892 2,052 2,322 2,451 2,508 2,838 3,078 3,268 3,483 3,564 3,762 4,257 4,644 4,902 5,643 5,676 6,156 6,966 7,353 7,524 8,514 8,987 9,804 11,286 12,771 13,932 14,706 16,929 17,028 17,974 22,059 22,572 25,542 26,961 29,412 33,858 35,948 38,313 44,118 51,084 53,922 66,177 67,716 76,626 80,883 88,236 107,844 132,354 153,252 161,766 242,649 264,708 323,532 485,298 727,947 970,596 1,455,894 and 2,911,788, with no remainder.
Since 2,911,788 cannot be divided by just 1 and 2,911,788, it is not a prime number.