A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1126356 can be evenly divided by 1 2 3 4 6 7 11 12 14 21 22 23 28 33 42 44 46 53 66 69 77 84 92 106 132 138 154 159 161 212 231 253 276 308 318 322 371 462 483 506 583 636 644 742 759 924 966 1,012 1,113 1,166 1,219 1,484 1,518 1,749 1,771 1,932 2,226 2,332 2,438 3,036 3,498 3,542 3,657 4,081 4,452 4,876 5,313 6,996 7,084 7,314 8,162 8,533 10,626 12,243 13,409 14,628 16,324 17,066 21,252 24,486 25,599 26,818 34,132 40,227 48,972 51,198 53,636 80,454 93,863 102,396 160,908 187,726 281,589 375,452 563,178 and 1,126,356, with no remainder.
Since 1,126,356 cannot be divided by just 1 and 1,126,356, it is not a prime number.