A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1161576 can be evenly divided by 1 2 3 4 6 8 9 12 13 17 18 24 26 34 36 39 51 52 68 72 73 78 102 104 117 136 146 153 156 204 219 221 234 292 306 312 408 438 442 468 584 612 657 663 876 884 936 949 1,224 1,241 1,314 1,326 1,752 1,768 1,898 1,989 2,482 2,628 2,652 2,847 3,723 3,796 3,978 4,964 5,256 5,304 5,694 7,446 7,592 7,956 8,541 9,928 11,169 11,388 14,892 15,912 16,133 17,082 22,338 22,776 29,784 32,266 34,164 44,676 48,399 64,532 68,328 89,352 96,798 129,064 145,197 193,596 290,394 387,192 580,788 and 1,161,576, with no remainder.
Since 1,161,576 cannot be divided by just 1 and 1,161,576, it is not a prime number.