A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3172848 can be evenly divided by 1 2 3 4 6 7 8 12 14 16 19 21 24 28 38 42 48 49 56 57 71 76 84 98 112 114 133 142 147 152 168 196 213 228 266 284 294 304 336 392 399 426 456 497 532 568 588 784 798 852 912 931 994 1,064 1,136 1,176 1,349 1,491 1,596 1,704 1,862 1,988 2,128 2,352 2,698 2,793 2,982 3,192 3,408 3,479 3,724 3,976 4,047 5,396 5,586 5,964 6,384 6,958 7,448 7,952 8,094 9,443 10,437 10,792 11,172 11,928 13,916 14,896 16,188 18,886 20,874 21,584 22,344 23,856 27,832 28,329 32,376 37,772 41,748 44,688 55,664 56,658 64,752 66,101 75,544 83,496 113,316 132,202 151,088 166,992 198,303 226,632 264,404 396,606 453,264 528,808 793,212 1,057,616 1,586,424 and 3,172,848, with no remainder.
Since 3,172,848 cannot be divided by just 1 and 3,172,848, it is not a prime number.