A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 961740 can be evenly divided by 1 2 3 4 5 6 9 10 12 13 15 18 20 26 27 30 36 39 45 52 54 60 65 78 90 108 117 130 135 137 156 180 195 234 260 270 274 351 390 411 468 540 548 585 685 702 780 822 1,170 1,233 1,370 1,404 1,644 1,755 1,781 2,055 2,340 2,466 2,740 3,510 3,562 3,699 4,110 4,932 5,343 6,165 7,020 7,124 7,398 8,220 8,905 10,686 12,330 14,796 16,029 17,810 18,495 21,372 24,660 26,715 32,058 35,620 36,990 48,087 53,430 64,116 73,980 80,145 96,174 106,860 160,290 192,348 240,435 320,580 480,870 and 961,740, with no remainder.
Since 961,740 cannot be divided by just 1 and 961,740, it is not a prime number.