A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6207720 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 17 20 24 30 34 40 51 60 68 85 102 120 136 170 179 204 255 289 340 358 408 510 537 578 680 716 867 895 1,020 1,074 1,156 1,432 1,445 1,734 1,790 2,040 2,148 2,312 2,685 2,890 3,043 3,468 3,580 4,296 4,335 5,370 5,780 6,086 6,936 7,160 8,670 9,129 10,740 11,560 12,172 15,215 17,340 18,258 21,480 24,344 30,430 34,680 36,516 45,645 51,731 60,860 73,032 91,290 103,462 121,720 155,193 182,580 206,924 258,655 310,386 365,160 413,848 517,310 620,772 775,965 1,034,620 1,241,544 1,551,930 2,069,240 3,103,860 and 6,207,720, with no remainder.
Since 6,207,720 cannot be divided by just 1 and 6,207,720, it is not a prime number.