A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3965148 can be evenly divided by 1 2 3 4 6 9 11 12 17 18 19 22 31 33 34 36 38 44 51 57 62 66 68 76 93 99 102 114 124 132 153 171 186 187 198 204 209 228 279 306 323 341 342 372 374 396 418 527 558 561 589 612 627 646 682 684 748 836 969 1,023 1,054 1,116 1,122 1,178 1,254 1,292 1,364 1,581 1,683 1,767 1,881 1,938 2,046 2,108 2,244 2,356 2,508 2,907 3,069 3,162 3,366 3,534 3,553 3,762 3,876 4,092 4,743 5,301 5,797 5,814 6,138 6,324 6,479 6,732 7,068 7,106 7,524 9,486 10,013 10,602 10,659 11,594 11,628 12,276 12,958 14,212 17,391 18,972 19,437 20,026 21,204 21,318 23,188 25,916 30,039 31,977 34,782 38,874 40,052 42,636 52,173 58,311 60,078 63,954 69,564 77,748 90,117 104,346 110,143 116,622 120,156 127,908 180,234 208,692 220,286 233,244 330,429 360,468 440,572 660,858 991,287 1,321,716 1,982,574 and 3,965,148, with no remainder.
Since 3,965,148 cannot be divided by just 1 and 3,965,148, it is not a prime number.