A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1279460 can be evenly divided by 1 2 4 5 7 10 13 14 19 20 26 28 35 37 38 52 65 70 74 76 91 95 130 133 140 148 182 185 190 247 259 260 266 364 370 380 455 481 494 518 532 665 703 740 910 962 988 1,036 1,235 1,295 1,330 1,406 1,729 1,820 1,924 2,405 2,470 2,590 2,660 2,812 3,367 3,458 3,515 4,810 4,921 4,940 5,180 6,734 6,916 7,030 8,645 9,139 9,620 9,842 13,468 14,060 16,835 17,290 18,278 19,684 24,605 33,670 34,580 36,556 45,695 49,210 63,973 67,340 91,390 98,420 127,946 182,780 255,892 319,865 639,730 and 1,279,460, with no remainder.
Since 1,279,460 cannot be divided by just 1 and 1,279,460, it is not a prime number.