A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 667590 can be evenly divided by 1 2 3 5 6 7 10 11 14 15 17 21 22 30 33 34 35 42 51 55 66 70 77 85 102 105 110 119 154 165 170 187 210 231 238 255 289 330 357 374 385 462 510 561 578 595 714 770 867 935 1,122 1,155 1,190 1,309 1,445 1,734 1,785 1,870 2,023 2,310 2,618 2,805 2,890 3,179 3,570 3,927 4,046 4,335 5,610 6,069 6,358 6,545 7,854 8,670 9,537 10,115 12,138 13,090 15,895 19,074 19,635 20,230 22,253 30,345 31,790 39,270 44,506 47,685 60,690 66,759 95,370 111,265 133,518 222,530 333,795 and 667,590, with no remainder.
Since 667,590 cannot be divided by just 1 and 667,590, it is not a prime number.