A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1687224 can be evenly divided by 1 2 3 4 6 7 8 11 12 14 21 22 24 28 33 42 44 56 66 77 83 84 88 121 132 154 166 168 231 242 249 264 308 332 363 462 484 498 581 616 664 726 847 913 924 968 996 1,162 1,452 1,694 1,743 1,826 1,848 1,992 2,324 2,541 2,739 2,904 3,388 3,486 3,652 4,648 5,082 5,478 6,391 6,776 6,972 7,304 10,043 10,164 10,956 12,782 13,944 19,173 20,086 20,328 21,912 25,564 30,129 38,346 40,172 51,128 60,258 70,301 76,692 80,344 120,516 140,602 153,384 210,903 241,032 281,204 421,806 562,408 843,612 and 1,687,224, with no remainder.
Since 1,687,224 cannot be divided by just 1 and 1,687,224, it is not a prime number.