A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2552760 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 14 15 18 20 21 24 28 30 35 36 40 42 45 56 60 63 70 72 84 90 105 120 126 140 168 180 210 252 280 315 360 420 504 630 840 1,013 1,260 2,026 2,520 3,039 4,052 5,065 6,078 7,091 8,104 9,117 10,130 12,156 14,182 15,195 18,234 20,260 21,273 24,312 28,364 30,390 35,455 36,468 40,520 42,546 45,585 56,728 60,780 63,819 70,910 72,936 85,092 91,170 106,365 121,560 127,638 141,820 170,184 182,340 212,730 255,276 283,640 319,095 364,680 425,460 510,552 638,190 850,920 1,276,380 and 2,552,760, with no remainder.
Since 2,552,760 cannot be divided by just 1 and 2,552,760, it is not a prime number.