A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1000776 can be evenly divided by 1 2 3 4 6 7 8 12 14 21 23 24 28 37 42 46 49 56 69 74 84 92 98 111 138 147 148 161 168 184 196 222 259 276 294 296 322 392 444 483 518 552 588 644 777 851 888 966 1,036 1,127 1,176 1,288 1,554 1,702 1,813 1,932 2,072 2,254 2,553 3,108 3,381 3,404 3,626 3,864 4,508 5,106 5,439 5,957 6,216 6,762 6,808 7,252 9,016 10,212 10,878 11,914 13,524 14,504 17,871 20,424 21,756 23,828 27,048 35,742 41,699 43,512 47,656 71,484 83,398 125,097 142,968 166,796 250,194 333,592 500,388 and 1,000,776, with no remainder.
Since 1,000,776 cannot be divided by just 1 and 1,000,776, it is not a prime number.