A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2179224 can be evenly divided by 1 2 3 4 6 8 9 12 18 19 24 27 36 38 54 57 59 72 76 81 108 114 118 152 162 171 177 216 228 236 243 324 342 354 456 472 486 513 531 648 684 708 972 1,026 1,062 1,121 1,368 1,416 1,539 1,593 1,944 2,052 2,124 2,242 3,078 3,186 3,363 4,104 4,248 4,484 4,617 4,779 6,156 6,372 6,726 8,968 9,234 9,558 10,089 12,312 12,744 13,452 14,337 18,468 19,116 20,178 26,904 28,674 30,267 36,936 38,232 40,356 57,348 60,534 80,712 90,801 114,696 121,068 181,602 242,136 272,403 363,204 544,806 726,408 1,089,612 and 2,179,224, with no remainder.
Since 2,179,224 cannot be divided by just 1 and 2,179,224, it is not a prime number.