A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1575252 can be evenly divided by 1 2 3 4 6 7 9 12 14 18 19 21 28 36 38 42 47 49 57 63 76 84 94 98 114 126 133 141 147 171 188 196 228 252 266 282 294 329 342 399 423 441 532 564 588 658 684 798 846 882 893 931 987 1,197 1,316 1,596 1,692 1,764 1,786 1,862 1,974 2,303 2,394 2,679 2,793 2,961 3,572 3,724 3,948 4,606 4,788 5,358 5,586 5,922 6,251 6,909 8,037 8,379 9,212 10,716 11,172 11,844 12,502 13,818 16,074 16,758 18,753 20,727 25,004 27,636 32,148 33,516 37,506 41,454 43,757 56,259 75,012 82,908 87,514 112,518 131,271 175,028 225,036 262,542 393,813 525,084 787,626 and 1,575,252, with no remainder.
Since 1,575,252 cannot be divided by just 1 and 1,575,252, it is not a prime number.