A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1542912 can be evenly divided by 1 2 3 4 6 7 8 12 14 16 21 24 28 32 41 42 48 49 56 64 82 84 96 98 112 123 128 147 164 168 192 196 224 246 256 287 294 328 336 384 392 448 492 574 588 656 672 768 784 861 896 984 1,148 1,176 1,312 1,344 1,568 1,722 1,792 1,968 2,009 2,296 2,352 2,624 2,688 3,136 3,444 3,936 4,018 4,592 4,704 5,248 5,376 6,027 6,272 6,888 7,872 8,036 9,184 9,408 10,496 12,054 12,544 13,776 15,744 16,072 18,368 18,816 24,108 27,552 31,488 32,144 36,736 37,632 48,216 55,104 64,288 73,472 96,432 110,208 128,576 192,864 220,416 257,152 385,728 514,304 771,456 and 1,542,912, with no remainder.
Since 1,542,912 cannot be divided by just 1 and 1,542,912, it is not a prime number.