A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1519620 can be evenly divided by 1 2 3 4 5 6 10 12 15 19 20 30 31 38 43 57 60 62 76 86 93 95 114 124 129 155 172 186 190 215 228 258 285 310 372 380 430 465 516 570 589 620 645 817 860 930 1,140 1,178 1,290 1,333 1,634 1,767 1,860 2,356 2,451 2,580 2,666 2,945 3,268 3,534 3,999 4,085 4,902 5,332 5,890 6,665 7,068 7,998 8,170 8,835 9,804 11,780 12,255 13,330 15,996 16,340 17,670 19,995 24,510 25,327 26,660 35,340 39,990 49,020 50,654 75,981 79,980 101,308 126,635 151,962 253,270 303,924 379,905 506,540 759,810 and 1,519,620, with no remainder.
Since 1,519,620 cannot be divided by just 1 and 1,519,620, it is not a prime number.