A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 823536 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 19 21 24 28 36 38 42 43 48 56 57 63 72 76 84 86 112 114 126 129 133 144 152 168 171 172 228 252 258 266 301 304 336 342 344 387 399 456 504 516 532 602 684 688 774 798 817 903 912 1,008 1,032 1,064 1,197 1,204 1,368 1,548 1,596 1,634 1,806 2,064 2,128 2,394 2,408 2,451 2,709 2,736 3,096 3,192 3,268 3,612 4,788 4,816 4,902 5,418 5,719 6,192 6,384 6,536 7,224 7,353 9,576 9,804 10,836 11,438 13,072 14,448 14,706 17,157 19,152 19,608 21,672 22,876 29,412 34,314 39,216 43,344 45,752 51,471 58,824 68,628 91,504 102,942 117,648 137,256 205,884 274,512 411,768 and 823,536, with no remainder.
Since 823,536 cannot be divided by just 1 and 823,536, it is not a prime number.