A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 5285385 can be evenly divided by 1 3 5 7 9 15 17 21 27 35 45 47 49 51 63 85 105 119 135 141 147 153 189 235 245 255 315 329 357 423 441 459 595 705 735 765 799 833 945 987 1,071 1,269 1,323 1,645 1,785 2,115 2,205 2,295 2,303 2,397 2,499 2,961 3,213 3,995 4,165 4,935 5,355 5,593 6,345 6,615 6,909 7,191 7,497 8,883 11,515 11,985 12,495 14,805 16,065 16,779 20,727 21,573 22,491 27,965 34,545 35,955 37,485 39,151 44,415 50,337 62,181 83,895 103,635 107,865 112,455 117,453 151,011 195,755 251,685 310,905 352,359 587,265 755,055 1,057,077 1,761,795 and 5,285,385, with no remainder.
Since 5,285,385 cannot be divided by just 1 and 5,285,385, it is not a prime number.