A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2501388 can be evenly divided by 1 2 3 4 6 9 12 18 19 23 27 36 38 46 53 54 57 69 76 92 106 108 114 138 159 171 207 212 228 276 318 342 414 437 477 513 621 636 684 828 874 954 1,007 1,026 1,219 1,242 1,311 1,431 1,748 1,908 2,014 2,052 2,438 2,484 2,622 2,862 3,021 3,657 3,933 4,028 4,876 5,244 5,724 6,042 7,314 7,866 9,063 10,971 11,799 12,084 14,628 15,732 18,126 21,942 23,161 23,598 27,189 32,913 36,252 43,884 46,322 47,196 54,378 65,826 69,483 92,644 108,756 131,652 138,966 208,449 277,932 416,898 625,347 833,796 1,250,694 and 2,501,388, with no remainder.
Since 2,501,388 cannot be divided by just 1 and 2,501,388, it is not a prime number.