A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 4221525 can be evenly divided by 1 3 5 7 11 15 17 21 25 33 35 43 51 55 75 77 85 105 119 129 165 175 187 215 231 255 275 301 357 385 425 473 525 561 595 645 731 825 903 935 1,075 1,155 1,275 1,309 1,419 1,505 1,785 1,925 2,193 2,365 2,805 2,975 3,225 3,311 3,655 3,927 4,515 4,675 5,117 5,775 6,545 7,095 7,525 8,041 8,925 9,933 10,965 11,825 14,025 15,351 16,555 18,275 19,635 22,575 24,123 25,585 32,725 35,475 40,205 49,665 54,825 56,287 76,755 82,775 98,175 120,615 127,925 168,861 201,025 248,325 281,435 383,775 603,075 844,305 1,407,175 and 4,221,525, with no remainder.
Since 4,221,525 cannot be divided by just 1 and 4,221,525, it is not a prime number.