A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3261960 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 13 15 17 18 20 24 26 30 34 36 39 40 41 45 51 52 60 65 68 72 78 82 85 90 102 104 117 120 123 130 136 153 156 164 170 180 195 204 205 221 234 246 255 260 306 312 328 340 360 369 390 408 410 442 468 492 510 520 533 585 612 615 663 680 697 738 765 780 820 884 936 984 1,020 1,066 1,105 1,170 1,224 1,230 1,326 1,394 1,476 1,530 1,560 1,599 1,640 1,768 1,845 1,989 2,040 2,091 2,132 2,210 2,340 2,460 2,652 2,665 2,788 2,952 3,060 3,198 3,315 3,485 3,690 3,978 4,182 4,264 4,420 4,680 4,797 4,920 5,304 5,330 5,576 6,120 6,273 6,396 6,630 6,970 7,380 7,956 7,995 8,364 8,840 9,061 9,594 9,945 10,455 10,660 12,546 12,792 13,260 13,940 14,760 15,912 15,990 16,728 18,122 19,188 19,890 20,910 21,320 23,985 25,092 26,520 27,183 27,880 31,365 31,980 36,244 38,376 39,780 41,820 45,305 47,970 50,184 54,366 62,730 63,960 72,488 79,560 81,549 83,640 90,610 95,940 108,732 125,460 135,915 163,098 181,220 191,880 217,464 250,920 271,830 326,196 362,440 407,745 543,660 652,392 815,490 1,087,320 1,630,980 and 3,261,960, with no remainder.
Since 3,261,960 cannot be divided by just 1 and 3,261,960, it is not a prime number.