A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 7417728 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 24 32 36 47 48 64 72 94 96 128 137 141 144 188 192 274 282 288 376 384 411 423 548 564 576 752 822 846 1,096 1,128 1,152 1,233 1,504 1,644 1,692 2,192 2,256 2,466 3,008 3,288 3,384 4,384 4,512 4,932 6,016 6,439 6,576 6,768 8,768 9,024 9,864 12,878 13,152 13,536 17,536 18,048 19,317 19,728 25,756 26,304 27,072 38,634 39,456 51,512 52,608 54,144 57,951 77,268 78,912 103,024 115,902 154,536 157,824 206,048 231,804 309,072 412,096 463,608 618,144 824,192 927,216 1,236,288 1,854,432 2,472,576 3,708,864 and 7,417,728, with no remainder.
Since 7,417,728 cannot be divided by just 1 and 7,417,728, it is not a prime number.