A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8171328 can be evenly divided by 1 2 3 4 6 8 11 12 16 22 24 32 33 44 48 53 64 66 73 88 96 106 132 146 159 176 192 212 219 264 292 318 352 424 438 528 583 584 636 704 803 848 876 1,056 1,166 1,168 1,272 1,606 1,696 1,749 1,752 2,112 2,332 2,336 2,409 2,544 3,212 3,392 3,498 3,504 3,869 4,664 4,672 4,818 5,088 6,424 6,996 7,008 7,738 9,328 9,636 10,176 11,607 12,848 13,992 14,016 15,476 18,656 19,272 23,214 25,696 27,984 30,952 37,312 38,544 42,559 46,428 51,392 55,968 61,904 77,088 85,118 92,856 111,936 123,808 127,677 154,176 170,236 185,712 247,616 255,354 340,472 371,424 510,708 680,944 742,848 1,021,416 1,361,888 2,042,832 2,723,776 4,085,664 and 8,171,328, with no remainder.
Since 8,171,328 cannot be divided by just 1 and 8,171,328, it is not a prime number.