A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 773850 can be evenly divided by 1 2 3 5 6 7 10 11 14 15 21 22 25 30 33 35 42 50 55 66 67 70 75 77 105 110 134 150 154 165 175 201 210 231 275 330 335 350 385 402 462 469 525 550 670 737 770 825 938 1,005 1,050 1,155 1,407 1,474 1,650 1,675 1,925 2,010 2,211 2,310 2,345 2,814 3,350 3,685 3,850 4,422 4,690 5,025 5,159 5,775 7,035 7,370 10,050 10,318 11,055 11,550 11,725 14,070 15,477 18,425 22,110 23,450 25,795 30,954 35,175 36,850 51,590 55,275 70,350 77,385 110,550 128,975 154,770 257,950 386,925 and 773,850, with no remainder.
Since 773,850 cannot be divided by just 1 and 773,850, it is not a prime number.