A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 660450 can be evenly divided by 1 2 3 5 6 7 10 14 15 17 21 25 30 34 35 37 42 50 51 70 74 75 85 102 105 111 119 150 170 175 185 210 222 238 255 259 350 357 370 425 510 518 525 555 595 629 714 777 850 925 1,050 1,110 1,190 1,258 1,275 1,295 1,554 1,785 1,850 1,887 2,550 2,590 2,775 2,975 3,145 3,570 3,774 3,885 4,403 5,550 5,950 6,290 6,475 7,770 8,806 8,925 9,435 12,950 13,209 15,725 17,850 18,870 19,425 22,015 26,418 31,450 38,850 44,030 47,175 66,045 94,350 110,075 132,090 220,150 330,225 and 660,450, with no remainder.
Since 660,450 cannot be divided by just 1 and 660,450, it is not a prime number.