A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1051776 can be evenly divided by 1 2 3 4 6 8 9 11 12 16 18 22 24 32 33 36 44 48 64 66 72 83 88 96 99 128 132 144 166 176 192 198 249 264 288 332 352 384 396 498 528 576 664 704 747 792 913 996 1,056 1,152 1,328 1,408 1,494 1,584 1,826 1,992 2,112 2,656 2,739 2,988 3,168 3,652 3,984 4,224 5,312 5,478 5,976 6,336 7,304 7,968 8,217 10,624 10,956 11,952 12,672 14,608 15,936 16,434 21,912 23,904 29,216 31,872 32,868 43,824 47,808 58,432 65,736 87,648 95,616 116,864 131,472 175,296 262,944 350,592 525,888 and 1,051,776, with no remainder.
Since 1,051,776 cannot be divided by just 1 and 1,051,776, it is not a prime number.