A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1170288 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 27 28 36 42 43 48 54 56 63 72 81 84 86 108 112 126 129 144 162 168 172 189 216 243 252 258 301 324 336 344 378 387 432 486 504 516 567 602 648 688 756 774 903 972 1,008 1,032 1,134 1,161 1,204 1,296 1,512 1,548 1,701 1,806 1,944 2,064 2,268 2,322 2,408 2,709 3,024 3,096 3,402 3,483 3,612 3,888 4,536 4,644 4,816 5,418 6,192 6,804 6,966 7,224 8,127 9,072 9,288 10,449 10,836 13,608 13,932 14,448 16,254 18,576 20,898 21,672 24,381 27,216 27,864 32,508 41,796 43,344 48,762 55,728 65,016 73,143 83,592 97,524 130,032 146,286 167,184 195,048 292,572 390,096 585,144 and 1,170,288, with no remainder.
Since 1,170,288 cannot be divided by just 1 and 1,170,288, it is not a prime number.