A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 5351220 can be evenly divided by 1 2 3 4 5 6 7 9 10 12 14 15 18 20 21 28 30 31 35 36 42 45 60 62 63 70 84 90 93 105 124 126 137 140 155 180 186 210 217 252 274 279 310 315 372 411 420 434 465 548 558 620 630 651 685 822 868 930 959 1,085 1,116 1,233 1,260 1,302 1,370 1,395 1,644 1,860 1,918 1,953 2,055 2,170 2,466 2,604 2,740 2,790 2,877 3,255 3,836 3,906 4,110 4,247 4,340 4,795 4,932 5,580 5,754 6,165 6,510 7,812 8,220 8,494 8,631 9,590 9,765 11,508 12,330 12,741 13,020 14,385 16,988 17,262 19,180 19,530 21,235 24,660 25,482 28,770 29,729 34,524 38,223 39,060 42,470 43,155 50,964 57,540 59,458 63,705 76,446 84,940 86,310 89,187 118,916 127,410 148,645 152,892 172,620 178,374 191,115 254,820 267,561 297,290 356,748 382,230 445,935 535,122 594,580 764,460 891,870 1,070,244 1,337,805 1,783,740 2,675,610 and 5,351,220, with no remainder.
Since 5,351,220 cannot be divided by just 1 and 5,351,220, it is not a prime number.