A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3747380 can be evenly divided by 1 2 4 5 7 10 13 14 20 26 28 29 35 52 58 65 70 71 91 116 130 140 142 145 182 203 260 284 290 355 364 377 406 455 497 580 710 754 812 910 923 994 1,015 1,420 1,508 1,820 1,846 1,885 1,988 2,030 2,059 2,485 2,639 3,692 3,770 4,060 4,118 4,615 4,970 5,278 6,461 7,540 8,236 9,230 9,940 10,295 10,556 12,922 13,195 14,413 18,460 20,590 25,844 26,390 26,767 28,826 32,305 41,180 52,780 53,534 57,652 64,610 72,065 107,068 129,220 133,835 144,130 187,369 267,670 288,260 374,738 535,340 749,476 936,845 1,873,690 and 3,747,380, with no remainder.
Since 3,747,380 cannot be divided by just 1 and 3,747,380, it is not a prime number.