A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 671220 can be evenly divided by 1 2 3 4 5 6 9 10 11 12 15 18 20 22 27 30 33 36 44 45 54 55 60 66 90 99 108 110 113 132 135 165 180 198 220 226 270 297 330 339 396 452 495 540 565 594 660 678 990 1,017 1,130 1,188 1,243 1,356 1,485 1,695 1,980 2,034 2,260 2,486 2,970 3,051 3,390 3,729 4,068 4,972 5,085 5,940 6,102 6,215 6,780 7,458 10,170 11,187 12,204 12,430 14,916 15,255 18,645 20,340 22,374 24,860 30,510 33,561 37,290 44,748 55,935 61,020 67,122 74,580 111,870 134,244 167,805 223,740 335,610 and 671,220, with no remainder.
Since 671,220 cannot be divided by just 1 and 671,220, it is not a prime number.