A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3221640 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 18 19 20 24 27 30 36 38 40 45 54 57 60 72 76 90 95 108 114 120 135 152 157 171 180 190 216 228 270 285 314 342 360 380 456 471 513 540 570 628 684 760 785 855 942 1,026 1,080 1,140 1,256 1,368 1,413 1,570 1,710 1,884 2,052 2,280 2,355 2,565 2,826 2,983 3,140 3,420 3,768 4,104 4,239 4,710 5,130 5,652 5,966 6,280 6,840 7,065 8,478 8,949 9,420 10,260 11,304 11,932 14,130 14,915 16,956 17,898 18,840 20,520 21,195 23,864 26,847 28,260 29,830 33,912 35,796 42,390 44,745 53,694 56,520 59,660 71,592 80,541 84,780 89,490 107,388 119,320 134,235 161,082 169,560 178,980 214,776 268,470 322,164 357,960 402,705 536,940 644,328 805,410 1,073,880 1,610,820 and 3,221,640, with no remainder.
Since 3,221,640 cannot be divided by just 1 and 3,221,640, it is not a prime number.