A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1564416 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 28 32 36 42 48 56 63 64 72 84 96 97 112 126 128 144 168 192 194 224 252 256 288 291 336 384 388 448 504 576 582 672 679 768 776 873 896 1,008 1,152 1,164 1,344 1,358 1,552 1,746 1,792 2,016 2,037 2,304 2,328 2,688 2,716 3,104 3,492 4,032 4,074 4,656 5,376 5,432 6,111 6,208 6,984 8,064 8,148 9,312 10,864 12,222 12,416 13,968 16,128 16,296 18,624 21,728 24,444 24,832 27,936 32,592 37,248 43,456 48,888 55,872 65,184 74,496 86,912 97,776 111,744 130,368 173,824 195,552 223,488 260,736 391,104 521,472 782,208 and 1,564,416, with no remainder.
Since 1,564,416 cannot be divided by just 1 and 1,564,416, it is not a prime number.