A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 715176 can be evenly divided by 1 2 3 4 6 7 8 9 11 12 14 18 21 22 24 27 28 33 36 42 43 44 54 56 63 66 72 77 84 86 88 99 108 126 129 132 154 168 172 189 198 216 231 252 258 264 297 301 308 344 378 387 396 462 473 504 516 594 602 616 693 756 774 792 903 924 946 1,032 1,161 1,188 1,204 1,386 1,419 1,512 1,548 1,806 1,848 1,892 2,079 2,322 2,376 2,408 2,709 2,772 2,838 3,096 3,311 3,612 3,784 4,158 4,257 4,644 5,418 5,544 5,676 6,622 7,224 8,127 8,316 8,514 9,288 9,933 10,836 11,352 12,771 13,244 16,254 16,632 17,028 19,866 21,672 25,542 26,488 29,799 32,508 34,056 39,732 51,084 59,598 65,016 79,464 89,397 102,168 119,196 178,794 238,392 357,588 and 715,176, with no remainder.
Since 715,176 cannot be divided by just 1 and 715,176, it is not a prime number.