A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1059660 can be evenly divided by 1 2 3 4 5 6 7 9 10 12 14 15 18 20 21 28 29 30 35 36 42 45 58 60 63 70 84 87 90 105 116 126 140 145 174 180 203 210 252 261 290 315 348 406 420 435 522 580 609 630 812 841 870 1,015 1,044 1,218 1,260 1,305 1,682 1,740 1,827 2,030 2,436 2,523 2,610 3,045 3,364 3,654 4,060 4,205 5,046 5,220 5,887 6,090 7,308 7,569 8,410 9,135 10,092 11,774 12,180 12,615 15,138 16,820 17,661 18,270 23,548 25,230 29,435 30,276 35,322 36,540 37,845 50,460 52,983 58,870 70,644 75,690 88,305 105,966 117,740 151,380 176,610 211,932 264,915 353,220 529,830 and 1,059,660, with no remainder.
Since 1,059,660 cannot be divided by just 1 and 1,059,660, it is not a prime number.