A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 7378020 can be evenly divided by 1 2 3 4 5 6 9 10 12 13 15 18 20 26 27 30 36 39 45 52 54 60 65 78 90 108 117 130 135 156 180 195 234 260 270 351 390 468 540 585 702 780 1,051 1,170 1,404 1,755 2,102 2,340 3,153 3,510 4,204 5,255 6,306 7,020 9,459 10,510 12,612 13,663 15,765 18,918 21,020 27,326 28,377 31,530 37,836 40,989 47,295 54,652 56,754 63,060 68,315 81,978 94,590 113,508 122,967 136,630 141,885 163,956 189,180 204,945 245,934 273,260 283,770 368,901 409,890 491,868 567,540 614,835 737,802 819,780 1,229,670 1,475,604 1,844,505 2,459,340 3,689,010 and 7,378,020, with no remainder.
Since 7,378,020 cannot be divided by just 1 and 7,378,020, it is not a prime number.