A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1372896 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 27 28 32 36 42 48 54 56 63 72 84 96 108 112 126 144 168 189 216 224 227 252 288 336 378 432 454 504 672 681 756 864 908 1,008 1,362 1,512 1,589 1,816 2,016 2,043 2,724 3,024 3,178 3,632 4,086 4,767 5,448 6,048 6,129 6,356 7,264 8,172 9,534 10,896 12,258 12,712 14,301 16,344 19,068 21,792 24,516 25,424 28,602 32,688 38,136 42,903 49,032 50,848 57,204 65,376 76,272 85,806 98,064 114,408 152,544 171,612 196,128 228,816 343,224 457,632 686,448 and 1,372,896, with no remainder.
Since 1,372,896 cannot be divided by just 1 and 1,372,896, it is not a prime number.