A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1724688 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 28 29 36 42 48 56 58 59 63 72 84 87 112 116 118 126 144 168 174 177 203 232 236 252 261 336 348 354 406 413 464 472 504 522 531 609 696 708 812 826 944 1,008 1,044 1,062 1,218 1,239 1,392 1,416 1,624 1,652 1,711 1,827 2,088 2,124 2,436 2,478 2,832 3,248 3,304 3,422 3,654 3,717 4,176 4,248 4,872 4,956 5,133 6,608 6,844 7,308 7,434 8,496 9,744 9,912 10,266 11,977 13,688 14,616 14,868 15,399 19,824 20,532 23,954 27,376 29,232 29,736 30,798 35,931 41,064 47,908 59,472 61,596 71,862 82,128 95,816 107,793 123,192 143,724 191,632 215,586 246,384 287,448 431,172 574,896 862,344 and 1,724,688, with no remainder.
Since 1,724,688 cannot be divided by just 1 and 1,724,688, it is not a prime number.